FIELD

[0001] Various example embodiments relate in general to communication networks, such as core networks of cellular communication systems, and more specifically, to improving authorization in such networks.

BACKGROUND

[0002] Authorization is needed in various communication networks to ensure that only users and network entities that have a right to access certain services can do that. Proper authorization needs to be ensured for example in core networks of cellular communication systems, such as in 5 G core networks developed by the 3rd Generation Partnership Project, 3 GPP. The 3 GPP still develops 5G core networks and there is a need to provide improved methods, apparatuses and computer programs for improving authorization in 5G core networks. Such improvements may be useful in other communication networks as well.

SUMMARY

[0003] According to some aspects, there is provided the subject-matter of the independent claims. Some example embodiments are defined in the dependent claims.

[0004] The scope of protection sought for various example embodiments of the invention is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various example embodiments of the invention.

[0005] According to a first aspect of the present invention, there is provided an apparatus comprising at least one processing core, at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processing core, cause the apparatus at least to perform transmit, by a first network function, an access token request on behalf of a second network function to an authorization server, the access token request concerning accessing services of a third network function and comprising information related to the second network function or an application function, receive, by the first network function, an access token from the authorization server, the access token comprising information about a subscribing network function and transmit, by the first network function, a subscription request to the third network function on behalf of the second network function, the subscription request comprising said information related to the second network function or the application function and the access token comprising said information about the subscribing network function.

[0006] In some example embodiments of the first aspect, the at least one memory and the computer program code may be configured to, with the at least one processing core, further cause the apparatus to perform, receive a subscription response indicating that the subscription request has not been accepted when said information related to the second network function or the application function does not correspond to said information about the subscribing network function in the access token.

[0007] In some example embodiments of the first aspect, the at least one memory and the computer program code may be configured to, with the at least one processing core, further cause the apparatus to perform, receive a subscription response indicating that the subscription request has been accepted when said information related to the second network function or the application function corresponds to said information about the subscribing network function in the access token.

[0008] According to a second aspect of the present invention, there is provided an apparatus comprising at least one processing core, at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processing core, cause the apparatus at least to perform receive, by an authorization server, an access token request from a first network function, the access token request comprising information related to a second network function or an application function and concerning accessing services of a third network function, and upon determining that the second network function is authorized to access the services of the third network function, transmit by the authorization server an access token to the first network function, the access token comprising information about a subscribing network function.

[0009] In some example embodiments of the second aspect, the at least one memory and the computer program code may be configured to, with the at least one processing core, further cause the apparatus to perform, transmit the access token response upon determining that the second network function or the application function is authorized to access the services of the third network function.

[0010] In some example embodiments of the second aspect, the at least one memory and the computer program code may be configured to, with the at least one processing core, further cause the apparatus to perform, sign, by the authorization server, the access token using a private key of the authorization server.

[0011] According to a third aspect of the present invention, there is provided an apparatus comprising at least one processing core, at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processing core, cause the apparatus at least to perform receive, by a third network function, a subscription request from a first network function, the subscription request comprising information related to a second network function or an application function and an access token signed by an authorization server, the access token comprising information about a subscribing network function and depending on whether the access token is valid, transmit by the third network function a subscription response to the first network function to indicate whether the second network function or the application function is authorized to access services of the third network function or not.

[0012] In some example embodiments of the third aspect, the at least one memory and the computer program code may be configured to, with the at least one processing core, further cause the apparatus to perform, decide that the access token is not valid when said information related to the second network function or the application function does not correspond to said information about the subscribing network function and transmit the subscription response to the first network function to indicate that the subscription request has not been accepted.

[0013] In some example embodiments of the third aspect, the at least one memory and the computer program code may be configured to, with the at least one processing core, further cause the apparatus to perform, decide that the access token is valid when said information related to the second network function or the application function corresponds to said information about the subscribing network function and transmit the subscription response to the first network function to indicate that the subscription request has been accepted. [0014] Example embodiments of the first, the second or the third aspect may comprise at least one feature from the following bulleted list:

• said information related to the second network function comprises information about an identity of the second network function;

• said information about the identity of the second network function comprises an instance identity and/or a set identity of the second network function;

• said information related to the second network function corresponds to said information about the subscribing network function;

• wherein the second network function is the subscribing network function originally requesting a subscription to the services of the third network function;

• said information related to the application function comprises information about an identity of the application function;

• said information related to the application function corresponds to said information about the subscribing network function;

• the application function is the subscribing network function originally requesting a subscription to the services of the third network function via the second network function;

• the second network function and the authorization server operate according to at least one standard specification defined by a 3 ^rd Generation Partnership Project, 3GPP; and

• the at least one standard specification is a 5G standard.

[0015] According to a fourth aspect of the present invention, there is provided a method, comprising transmitting, by a first network function, an access token request on behalf of a second network function to an authorization server, the access token request concerning accessing services of a third network function and comprising information related to the second network function or an application function, receiving, by the first network function, an access token from the authorization server, the access token comprising information about a subscribing network function and transmitting, by the first network function, a subscription request to the third network function on behalf of the second network function, the subscription request comprising said information related to the second network function or the application function and the access token comprising said information about the subscribing network function.

[0016] According to a fifth aspect of the present invention, there is provided a method comprising, receiving, by an authorization server, an access token request from a first network function, the access token request comprising information related to a second network function or an application function and concerning accessing services of a third network function and upon determining that the second network function is authorized to access the services of the third network function, transmitting by the authorization server an access token to the first network function, the access token comprising information about a subscribing network function.

[0017] According to a sixth aspect of the present invention, there is provided a method comprising receiving, by a third network function, a subscription request from a first network function, the subscription request comprising information related to a second network function or an application function and an access token signed by an authorization server, the access token comprising information about a subscribing network function and depending on whether the access token is valid, transmitting by the third network function a subscription response to the first network function to indicate whether the second network function or the application function is authorized to access services of the third network function or not.

[0018] According to a seventh aspect of the present invention, there is provided an apparatus, comprising means for transmitting, by a first network function, an access token request on behalf of a second network function to an authorization server, the access token request concerning accessing services of a third network function and comprising information related to the second network function or an application function, means for receiving, by the first network function, an access token from the authorization server, the access token comprising information about a subscribing network function and means for transmitting, by the first network function, a subscription request to the third network function on behalf of the second network function, the subscription request comprising said information related to the second network function or the application function and the access token comprising said information about the subscribing network function. [0019] According to an eighth aspect of the present invention, there is provided an apparatus, comprising means for receiving, by an authorization server, an access token request from a first network function, the access token request comprising information related to a second network function or an application function and concerning accessing services of a third network function and means for transmitting by the authorization server, upon determining that the second network function is authorized to access the services of the third network function, an access token to the first network function, the access token comprising information about a subscribing network function.

[0020] According to a ninth aspect of the present invention, there is provided an apparatus, comprising means for receiving, by a third network function, a subscription request from a first network function, the subscription request comprising information related to a second network function or an application function and an access token signed by an authorization server, the access token comprising information about a subscribing network function and means for transmitting by the third network function, depending on whether the access token is valid, a subscription response to the first network function to indicate whether the second network function or the application function is authorized to access services of the third network function or not.

[0021] According to a tenth aspect of the present invention, there is provided non- transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform the method of the fourth aspect. According to an eleventh aspect of the present invention, there is provided non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform the method of the fifth aspect. According to a twelfth aspect of the present invention, there is provided non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform the method of the sixth aspect.

[0022] According to a thirteenth aspect of the present invention, there is provided a computer program configured to perform the method of the fourth aspect. According to a fourteenth aspect of the present invention, there is provided a computer program configured to perform the method of the fifth aspect. According to a fifteenth aspect of the present invention, there is provided a computer program configured to perform the method of the sixth aspect.

BRIEF DESCRIPTION OF THE DRAWINGS [0023] FIGURE 1 illustrates an exemplary system in accordance with at least some example embodiments;

[0024] FIGURE 2 illustrates a first signalling example in accordance with at least some example embodiments;

[0025] FIGURE 3 illustrates a second signalling example in accordance with at least some example embodiments;

[0026] FIGURE 4 illustrates an example apparatus capable of supporting at least some example embodiments;

[0027] FIGURE 5 illustrates a flow graph of a first method in accordance with at least some example embodiments; [0028] FIGURE 6 illustrates a flow graph of a second method in accordance with at least some example embodiments; and

[0029] FIGURE 7 illustrates a flow graph of a third method in accordance with at least some example embodiments. EXAMPLE EMBODIMENTS

[0030] Authorization may be improved by the procedures described herein for example by enabling authorization of delegated subscription requests. A first Network Function, NF, may transmit an access token request on behalf of a second NF to an authorization server, to request access to services of a third NF. The access token request may comprise information related to the second NF or an Application Function, AF, such as information about an identity of the second NF or the AF. The authorization server may check whether the second NF or the AF is authorized to access the services of the third NF and if so, respond to the first NF by transmitting an access token comprising information about a subscribing NF, such as the second NF or the AF. [0031] The first NF may then transmit a subscription request to the third NF on behalf of the second NF, the subscription request also comprising said information related to the second NF or the AF and the access token, wherein the access token comprises said information about the subscribing NF. The third NF may validate the access token received from the first NF in the subscription request when said information related to the second NF or the AF corresponds to said information about the subscribing NF, and respond by transmitting a subscription response, the subscription response indicating that the second NF or the AF is authorized to access the services of the third NF. Thus, authorization of delegated subscription requests is enabled.

[0032] FIGURE 1 illustrates an exemplary system in accordance with at least some example embodiments of the present invention. The exemplary system of FIGURE 1 comprises two Public Land Mobile Networks, PLMNs, 110 and 112, each equipped with at least one NF, 120 and 122, respectively. AnNF may refer to an operational and/or a physical entity. An NF may be a specific network node or element, or a specific function or set of functions carried out by one or more entities, such as Virtual Network Elements, VNFs. At least some example embodiments of the present invention may be applied in containerized deployments as well. One physical node may be configured to perform plural NFs. Examples of such NFs include a (radio) access or resource control or management function, session management or control function, interworking, data management or storage function, authentication function or a combination of one or more of these functions.

[0033] In case of a 3 ^rd Generation Partnership Project, 3GPP, Service-Based Architecture, SB A, of 5G core networks, NFs may comprise at least some of an Access and Mobility Function, AMF, a Session Management Function, SMF, a Network Slice Selection Function, NSSF, a Network Exposure Function, NEF, a Network Repository Function, NRF, an Unified Data Management, UDM, an User Data Repository, UDR, an Unstructured Data Storage Function, UDSF, an Authentication Server Function, AUSF, a Policy Control Function, PCF, an AF, Operations Administration and Maintenance, OAM, and Network Data Analysis Function, NWDAF.

[0034] The PLMNs 110 and 112 may further comprise a Security Edge Protection Proxy, SEPP, 130 and 132, respectively. The SEPPs 130 and 132 may be configured to operate as a security edge node or gateway. The NFs may communicate with each other using representational state transfer Application Programming Interfaces, APIs. These may be known as Restful APIs.

[0035] An inter-PLMN interconnection allows secure communication between a service-consuming NF and a service-producing NF, referred to as a NFc 120 and a NFp 122 in FIGURE 1, respectively. A Service Communication Proxy, SCP, 150 may be deployed for indirect communication between network functions. The SCP 150 may be an intermediate function/element for assisting in routing of messages, such as control plane messages like Diameter Routing Agent, DRA, messages between NFs.

[0036] NF discovery and NF service discovery enable core network entities, such as the NFc 140 or the SCP 150, to discover a set of NF instance(s) andNF service instance(s) for a specific NF service or an NF type. The NRF is a function that is used to support the functionality of NFs and NF service discovery and status notification. The NRF may maintain an NF profile of available NF instances and their supported services. The NRF may notify about newly registered, updated, or deregistered NF instances along with its NF services to a subscribed NFc 120 or SCPc 150. Unless the expected NF and/or NF service information is locally configured on the requester NF, such as when the expected NF service or NF is in the same PLMN as the requester NF, the NF and NF service discovery may be implemented via the NRF. The NRF may be a logical function. The NRF may also support status notification. An NRF may be co-located together with an SCP.

[0037] In order for the NFc 120 or the SCPc 150 to obtain information about the NF and/or NF service(s) registered or configured in a PLMN/slice, the NFc 120 or the SCPc 150 may initiate, based on local configuration, a discovery procedure with the NRF 140c. The discovery procedure may be initiated by providing the type of the NF and optionally a list of the specific service(s) it is attempting to discover. The NFc 120 or the SCPc 150 may also provide other service parameters, such as slicing related information.

[0038] It is to be noted that at least some of the entities or nodes 120, 122, 130, 132, 140, 142, 150, 152 may act in both service-consuming and service-providing roles and that their structure may also be similar or identical, even though their role in the example of FIGURE 1 in delivery of a particular message is identified by use of the prefix “c” or “p” indicating whether they are acting for the service-consuming or service-producing NF. It is to be noted that instead of “c” and “p”, “v” for visited and “h” for home may be used to refer to at least some respective entities in the visited and home PLMNs.

[0039] In some example embodiments, OAuth based authorization and token exchange may be applied between the mobile networks. For instance, the NFc 120 may be an OAuth client and the NRFp 142 may operate as OAuth resource server, and both may be configured to support OAuth authorization framework as defined in RFC 6749.

[0040] In case of delegated subscriptions, a first NF, such as NFc 120 in FIGURE 1, may want to transmit a subscription request (e.g., an UDM subscription request) on behalf of a second NF, the subscription request concerning accessing services of a third NF, such as NFp 122 in FIGURE 1. However, in such a case it should be ensured that an authorization server, such as an NRF, is aware that the first NF wants to subscribe on behalf of the second NF and if the authorization server authorizes the subscription request, it also authorizes access to services of the third NF by the second NF, e.g., notifications from the third NF to the second NF. In other words, there is a need to ensure that the second NF, i.e., original NFc, requesting the subscription is authorized correctly. Similarly, there is a need to ensure that the authorization server may authorize delegated subscription when the subscribing NF is an AF.

[0041] Embodiments of the present invention therefore enable authorization of delegated subscriptions by making it possible for the authorization server to decide whether to authorize the subscription request, or not, for the second NF, i.e., the original subscribing NF. Without authorization of the authorization server the second NF will not be able to access the services of the third NF. Consequently, security gaps for subscribe/notify scenarios with delegated discovery may be avoided. The original subscribing NF may be authorized properly and given access rights to the requested services. Security gaps may be avoided similarly if the subscribing NF is the AF.

[0042] In some example embodiments, an access token API and access token claims, i.e., an access token request, may be enhanced for delegated subscriptions, wherein for example the first NF may create a subscription at a third NF on behalf of the second NF or the AF, i.e., the NF originally requesting the subscription, if authorized by the authorization server. Thus, the authorization server may control authorization of the second NF or the AF such that the second NF or the AF can access the services of the third NF, e.g., obtain notifications from the third NF, only if the second NF or the AF has been authorized.

[0043] The first NF, which needs to issue a subscription request to the third NF on behalf of the second NF, may add information related to the second NF or the AF to an access token request concerning accessing services of the third NF. The first NF may transmit the access token request to the authorization server, such as the NRF. The first NF may therefore indicate the original subscribing NF, i.e., the second NF or the AF, in the access token request. The authorization server may then determine whether the second NF or the AF is authorized to access the services of the third NF, for example to obtain notifications from the third NF.

[0044] If the second NF or the AF can be authorized, the authorization server may respond to the first NF by transmitting an access token signed by the authorization server, the access token comprising information about the subscribing NF. The first NF may then transmit a subscription request to the third NF on behalf of the second NF, the subscription request comprising said information related to the second NF or the AF and the access token comprising said information about the subscribing NF. If said information related to the second NF or the AF corresponds to said information about the subscribing NF, the third NF may validate the access token and transmit a subscription response to the first NF, the subscription response indicating that the second NF or the AF is authorized to access services of the third NF.

[0045] FIGURE 2 illustrates a first signalling example in accordance with at least some example embodiments. On the vertical axes are disposed, from the left to the right, first NF 202, second NF 204, third NF 206 and authentication server 208. Time advances from the top towards the bottom. FIGURE 2 illustrates an example, wherein first NF 202 may perform delegated subscription on behalf of second NF 204 for services of third NF 206. In some example embodiments, first NF 202 may be an UDM, second NF 204 may be an NEF, third NF 206 may be an AMF and authorization server 208 may be an NRF.

[0046] Before step 210, second NF 204 may determine that it would like to transmit a subscription request to first NF 202. Therefore, at step 210, second NF 204 may transmit an access token request concerning accessing services of first NF 202 to authorization server 208. Authorization server 208 may then authorize second NF 204 to send a subscription request towards first NF 202, to access the services of first NF 202, by transmitting an access token response to second NF 204. The access token response may comprise an access token signed by authorization server 208.

[0047] Upon receiving the access token from authorization server 208, second NF 204 may transmit at step 220 a subscription request concerning accessing services of first NF 202 towards first NF 202, e.g., with an authorization header carrying the access token. First NF 202 may then create a subscription for second NF 204 and respond to second NF 204 accordingly.

[0048] In some example embodiments, the subscription request transmitted by second NF 204 may comprise information related to second NF 204, such as information about an identity of second NF 204. Said information related to the identity of second NF 204 may be an instance identity (instancelD) and/or a set identity (setID) of second NF 204. For instance, the subscription request received from second NF 204 may comprise NFinstanceld = NF2 or NFsetId= NF2 Set ID and CallbackURI=NF2_URI. Alternatively, first NF 202 may derive said information related to second NF 204 during a Transport Layer Security, TLS, handshake (TLS authentication).

[0049] First NF 202 may also determine that it needs, or wants, to create a subscription at a new NFp, such as third NF 206, on behalf of second NF 204. That is to say, first NF 202 may determine that there is a need to perform delegated subscription on behalf of second NF 204. Upon determining that there is a need to create a subscription at third NF 206 on behalf of second NF 204, first NF 202 should forward the subscription request received from second NF 204 to third NF 206, e.g., with the notification callback URI that points to second NF 204. First NF 202 would also need to add an access token to the subscription request, which is to be transmitted to third NF 206.

[0050] At step 230, first NF 202 may transmit an access token request to authorization server 208, to request the access token for accessing services of third NF 206. First NF 202 may add information related to second NF 204, such as information about the identity of second NF 204, to the access token request. Said information related to second NF 204 may thus indicate the original subscribing NF, i.e., second NF 204, towards which third NF 206 would be authorized to provide services, for example to send notifications. Rest of the parameters used in the access token request may be defined in 3 GPP standard specification TS 29.510, section 6.3.5.2.4.

[0051] For instance, in some example embodiments, the access token request, such as Nnrf AccessToken API, may comprise the following information: grant type = client credentials, SubscribingNFInfo : NF2 (instance Id/Setld.. received in subscription request or derived by other means), Instanceld (source) NF1, targetNfType= NF3 and targetNfhistanceId= NF3. Other parameters may be added depending on a use case.

[0052] Upon receiving the access token request from first NF 202, authorization server 208, such as an NRF, may authorize first NF 202 to transmit a subscription request to third NF 206 and third NF 206 to provide services to first NF 202, .e.g., third NF 206 may be allowed to send notifications towards first NF 202. Alternatively, or in addition, authorization server 208 may authorize first NF 202 to transmit a subscription request to third NF 206 on behalf of second NF 204, e.g., second NF 204 may be allowed to receive notifications from third NF 206 and third NF 206 to provide services to second NF 204, .e.g., third NF 206 may be allowed to send notifications towards second NF 202.

[0053] Authorization server 208 may, upon determining that first NF 202 and second NF 204 are authorized to access the services of third NF 206, generate a digitally signed access token. Authorization server 208 may also include information about a subscribing NF, such as second NF 204 if it is the original NF requesting the subscription to services of third NF 206, as a new claim in the access token. Authorization server 208 may then transmit the signed access token comprising said information about the subscribing NF to first NF 202. However, if first NF 202 or second NF 204 is not allowed to subscribe to services provided by third NF 206, authorization server 208 may reject the access token request.

[0054] If the authorization was granted, first NF 202 may transmit a subscription request to third NF 206 on behalf of second NF 204. The subscription request may comprise the access token signed by authorization server 208, wherein the access token may comprise said information about the subscribing NF, and the subscription request may comprise said information related to second NF 204, such as information about an identity of second NF 204 (e.g., instance identity or set identity of second NF 204, possibly received from second NF 204). The subscription request may comprise for example at least the following information: NFinstanceId/SetId= NF2 and CallbackURI=NF2 URI. [0055] Third NF 206, such as NFp, may then check whether said information related to second NF 204 corresponds to said information about the subscribing NF in the access token. That is to say, third NF 206 may determine whether the access token is valid and transmit a subscription response to first NF 202 to indicate whether second NF 204 is authorized to access services of third NF 206, or not.

[0056] If said information related to second NF 204 corresponds to, i.e. is the same as, said information about the subscribing NF in the access token, third NF 206 may decide that the access token is valid and accept the subscription request, and transmit a subscription response to first NF 202 to indicate that second NF 204 is authorized to access services of third NF 206, i.e., the subscription has been accepted. Third NF 206 may also store the callback URI information of second NF 204, which can be used later for transmitting notifications to second NF 204.

[0057] However, if said information related to second NF 204 does not correspond to, i.e., is not the same as, said information about the subscribing NF in the access token, third NF 206 may decide that the access token is not valid and reject the subscription request, and transmit a subscription response to first NF 202 to indicate that second NF 204 is not authorized to access services of third NF 206, i.e., the subscription request has not been accepted.

[0058] FIGURE 3 illustrates a second signalling example in accordance with at least some example embodiments. On the vertical axes are disposed, from the left to the right, first NF 302, second NF 304, third NF 306 and authentication server 308. Time advances from the top towards the bottom. FIGURE 3 also illustrates an example, wherein first NF 302 may perform delegated subscription on behalf of second NF 304. In some example embodiments, first NF 302 may be a first NFc, second NF 304 may be a second NFc, third NF 306 may be an NFp and authorization server 308 may be an hNRF.

[0059] At step 310, first NF 302 may receive a subscription request from second NF 304. The subscription request may comprise at least information related to second NF 304, such as information about an identity of second NF 304, and an access token. At step 315, first NF 302 may authorize the subscription request by validating the access token and decide to forward the subscription request to third NF 306. The subscription request received from second NF 304 may comprise for example at least the following information: NF2 instance/set ID, NF2 callbackURI, access token 1.

[0060] At step 320, first NF 302 may transmit an access token request to authorization server 308, such as an OAuth server like an NRF, to obtain a new access token to access services of third NF 306. That is to say, the access token request may be related to accessing services of third NF 306. The access token request may comprise said information related to second NF 304, such as information about an identity of second NF 304 (e.g., a new parameter called Subscribing NF Info may comprise NF Instance ID or NF Set ID of second NF 304 (obtained at step 310)). That is to say, said information related to second NF 304 may be information about a subscribing NF.

[0061] At step 325, authorization server 308 may check if first NF 302 can be authorized to delegate a subscription request to third NF 306 and second NF 304 can be authorized to access services of third NF 306, e.g., to obtain notifications from third NF 306. If said authorization checks are successful, authorization server 308 may create a digitally signed access token with said information about the subscribing NF, such as said information related to second NF 304 (e.g., with one additional claim called SubscribingNFInfo that identifies second NF 304).

[0062] In some example embodiments, authorization server 308 may check if first NF 302 can be authorized to delegate a subscription request to third NF 306 and second NF 304 can be authorized to access services of third NF 306 by configurations in NF profiles, which may be maintained by authorization server 308, such as an NRF. For instance, if the requested service is related to obtaining notifications, third NF 306 may maintain, at authorization server 308, its profile information of NF types that can receive notifications from it. Similarly, information about delegated subscription may be configured in the NF profile of second NF 304 or in the profile of first NF 302.

[0063] Upon determining that second NF 304 is authorized to access the services of third NF 306, authorization server 308 may, at step 330, transmit the access token comprising said information about the subscribing NF to first NF 302.

[0064] At step 340, first NF 302 may forward the subscription request comprising said information related to second NF 304 and the access token received at step 330 to third NF 306, wherein the access token is signed by authorization server 308 and comprises said information about the subscribing NF. Said information related to second NF 304 may comprise information about an identity of second NF 304, such as a NF instance ID or NF set ID of second NF 304. The subscription request may comprise a callback URI as well. [0065] In some example embodiments, the NF Set ID may be defined as in clause

28.12 in 3GPP standard specification TS 23.003. The NF instance ID may uniquely identify an NF instance. For instance, the format of the NF instance ID may be a Universally Unique Identifier, UUID, version 4, as described in IETF RFC 4122.

[0066] Third NF 306 may then validate the received access token, e.g., by checking that second NF 304 is authorized to access services of third NF 306, for example to receive notifications from third NF 306. Third NF may check that second NF 304 is authorized to access services of third NF 306 by comparing said information related to second NF 304 received in the subscription request to said information about the subscribing NF in the access token. [0067] If said information related to second NF 304 received in the subscription request corresponds to said information about the subscribing NF in the access token, third NF 306 may determine that second NF 304 is authorized to access services of third NF 306 and decide that the access token is valid. Third NF 306 may also transmit at step 350 a subscription response to first NF 302, the subscription response indicating that the subscription request has been accepted when said information related to the second NF 304 corresponds to said information about the subscribing NF. In such a case, third NF 306 may store the callback URI needed later, e.g., for transmitting a notification message to second NF 304.

[0068] At optional step 360, third NF 306 may for example transmit a notification to second NF 304 upon detecting that a required event has happened, if second NF 304 was authorized to access services of third NF 306. Said notification may be transmitted using the stored callback URI of second NF 304 for example.

[0069] Some example embodiments of the present invention may be applied for example in 3GPP standard specification TS 29.510, Section 6.3.5.2.4 “Type: AccessTokenClaims”, Table 6.3.5.2.4-1: “Definition of type AccessTokenClaims” by adding at least some of the following information:

• Attribute name: subscribingNFInstld, Data type: Nflnstanceld, P: C, Cardinality: 0...1, Description: This IE may be included if the NF requesting the access token, is delegating the subscribe request to the NF identified by the “aud” claim on behalf of another NF identified by this claim; and/or

• Attribute name: subscribingNFSetld, Data type: NfSetld, P: C, Cardinality: 0...1, Description: This IE may be included if the NF requesting the access token, is delegating the subscribe request to the NF identified by the “aud” claim, on behalf of a set of NFs identified by this claim.

• Attribute name: subscribingNFType, Data type: NfType, P: C, Cardinality: 0...1, Description: This IE may be included if the NF requesting the access token, is delegating the subscribe request to the NF identified by the “aud” claim, on behalf of another NF of NF type identified by this claim.

• Attribute name: subscribingAFId, Data type: String, P: C, Cardinality: 0...1, Description: This IE may be included if the NF requesting the access token, is delegating the subscribe request to the NF identified by the “aud” claim, on behalf of another NF for a request issued by an AF (Application Function) identified by this claim. [0070] In some example embodiments, an access token may be requested by first NF

302 for a delegated subscription on behalf of another NF identified by its NF type, such as the NF type of second NF 304. For instance, the NF type of second NF 304 may be signalled from second NF 304 to first NF 302 in the subscription request.

[0071] In some example embodiments, an access token may be requested by first NF 302 for a delegated subscription on behalf of another NF based upon an identity of an AF.

For instance, the identity of the AF may be signalled from second NF 304 to first NF 302 in the subscription request. In such a case, the AF may be the subscribing NF and embodiments of the present disclosure may be applied similarly as if second NF 304 would be the subscribing NF. [0072] As an example, the AF may issue a subscription request to second NF 304, such as an NEF. Second NF 304 may then issue a subscription request to first NF 302, such as an UDM and first NF 302 may transmit an access token request on behalf of second NF 304 to authorization server 308, the access token request comprising information related to the AF, such as an identity of the AF. First NF 302 may then delegate the subscription request to third NF, such as an AMF, upon receiving the access token comprising said information about the subscribing NF from authorization server 308, when the subscribing NF is the AF. Authorization server 308 can thus also grant authorization based on the identity of the AF.

[0073] FIGURE 4 illustrates an example apparatus capable of supporting at least some example embodiments. Illustrated is device 400, which may comprise, for example, an NFc, NFp or authorization server, or a device controlling functioning thereof. Comprised in device 400 is processor 410, which may comprise, for example, a single- or multi-core processor wherein a single-core processor comprises one processing core and a multi-core processor comprises more than one processing core. Processor 410 may comprise, in general, a control device. Processor 410 may comprise more than one processor. Processor 410 may be a control device. Processor 410 may comprise at least one Application-Specific Integrated Circuit, ASIC. Processor 410 may comprise at least one Field-Programmable Gate Array, FPGA. Processor 410 may comprise an Intel Xeon processor for example. Processor 410 may be means for performing method steps in device 400, such as determining, causing transmitting and causing receiving. Processor 410 may be configured, at least in part by computer instructions, to perform actions.

[0074] A processor may comprise circuitry, or be constituted as circuitry or circuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with example embodiments described herein. As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of hardware circuits and software, such as, as applicable: (i) a combination of analog and/or digital hardware circuit(s) with software/firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a network function, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0075] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0076] Device 400 may comprise memory 420. Memory 420 may comprise random- access memory and/or permanent memory. Memory 420 may comprise at least one RAM chip. Memory 420 may comprise solid-state, magnetic, optical and/or holographic memory, for example. Memory 420 may be at least in part accessible to processor 410. Memory 420 may be at least in part comprised in processor 410. Memory 420 may be means for storing information. Memory 420 may comprise computer instructions that processor 410 is configured to execute. When computer instructions configured to cause processor 410 to perform certain actions are stored in memory 420, and device 400 overall is configured to run under the direction of processor 410 using computer instructions from memory 420, processor 410 and/or its at least one processing core may be considered to be configured to perform said certain actions. Memory 420 may be at least in part comprised in processor 410. Memory 420 may be at least in part external to device 400 but accessible to device 400.

[0077] Device 400 may comprise a transmitter 430. Device 400 may comprise a receiver 440. Transmitter 430 and receiver 440 may be configured to transmit and receive, respectively, information in accordance with at least one cellular standard, such as a standard defined by the 3GPP. Transmitter 430 may comprise more than one transmitter. Receiver 440 may comprise more than one receiver. Transmitter 430 and/or receiver 440 may be configured to operate in accordance with a suitable communication standard.

[0078] Device 400 may comprise User Interface, UI, 450. UI 450 may comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing device 400 to vibrate, a speaker and a microphone. A user may be able to operate device 400 via UI 450, for example to configure device 400 and/or functions it runs.

[0079] Processor 410 may be furnished with a transmitter arranged to output information from processor 410, via electrical leads internal to device 400, to other devices comprised in device 400. Such a transmitter may comprise a serial bus transmitter arranged to, for example, output information via at least one electrical lead to memory 420 for storage therein. Alternatively to a serial bus, the transmitter may comprise a parallel bus transmitter. Likewise processor 410 may comprise a receiver arranged to receive information in processor 410, via electrical leads internal to device 400, from other devices comprised in device 400. Such a receiver may comprise a serial bus receiver arranged to, for example, receive information via at least one electrical lead from receiver 440 for processing in processor 410. Alternatively to a serial bus, the receiver may comprise a parallel bus receiver.

[0080] Device 400 may comprise further devices not illustrated in FIGURE 4. In some example embodiments, device 400 lacks at least one device described above. For example, device 400 may not have UI 450.

[0081] Processor 410, memory 420, transmitter 430, receiver 440 and/or UI 450 may be interconnected by electrical leads internal to device 400 in a multitude of different ways. For example, each of the aforementioned devices may be separately connected to a master bus internal to device 400, to allow for the devices to exchange information. However, as the skilled person will appreciate, this is only one example and depending on the example embodiment various ways of interconnecting at least two of the aforementioned devices may be selected without departing from the scope of the present invention.

[0082] FIGURE 5 is a flow graph of a first method in accordance with at least some example embodiments. The phases of the illustrated first method may be performed by a first NF, such as a NFc, or by a control device configured to control the functioning thereof, possibly when installed therein.

[0083] The first method may comprise, at step 510, transmitting, by a first NF, an access token request on behalf of a second NF to an authorization server, the access token request concerning accessing services of a third NF and comprising information related to the second NF or an AF. Also, the first method may comprise, at step 520, receiving, by the first NF, an access token from the authorization server, the access token comprising information about a subscribing NF. Finally, the first method may comprise, at step 530, transmitting, by the first NF, a subscription request to the third NF on behalf of the second NF, the subscription request comprising said information related to the second NF or the AF and the access token comprising said information about the subscribing NF.

[0084] FIGURE 6 is a flow graph of a second method in accordance with at least some example embodiments. The phases of the illustrated second method may be performed by an authorization server, such as an NRF, or by a control device configured to control the functioning thereof, possibly when installed therein.

[0085] The second method may comprise, at step 610, receiving, by an authorization server, an access token request from a first NF, the access token request comprising information related to a second NF or an AF and concerning accessing services of a third NF. The second method may also comprise, at step 620, transmitting by the authorization server an access token comprising information about a subscribing NF upon determining that the second NF is authorized to access the services of the third NF.

[0086] FIGURE 7 is a flow graph of a third method in accordance with at least some example embodiments. The phases of the illustrated third method may be performed by a third NF, such as a NFp or by a control device configured to control the functioning thereof, possibly when installed therein.

[0087] The third method may comprise, at step 710, receiving, by a third NF, a subscription request from a first NF, the subscription request comprising information related to a second NF or an AF and an access token signed by an authorization server, the access token comprising information about a subscribing NF. The third method may also comprise, at step 720, depending on whether the access token is valid, transmitting by the third NF a subscription response to the first NF to indicate whether the second NF or the AF is authorized to access services of the third NF or not.

[0088] It is to be understood that the example embodiments disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular example embodiments only and is not intended to be limiting.

[0089] Reference throughout this specification to one example embodiment or an example embodiment means that a particular feature, structure, or characteristic described in connection with the example embodiment is included in at least one example embodiment. Thus, appearances of the phrases “in one example embodiment” or “in an example embodiment” in various places throughout this specification are not necessarily all referring to the same example embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0090] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various example embodiments and examples may be referred to herein along with alternatives for the various components thereof. It is understood that such example embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations.

[0091] In an example embodiment, an apparatus, such as, for example, an NFc, NFp or authorization server, or a device controlling functioning thereof, may comprise means for carrying out the example embodiments described above and any combination thereof.

[0092] In an example embodiment, a computer program may be configured to cause a method in accordance with the example embodiments described above and any combination thereof. In an exemplary example embodiment, a computer program product, embodied on a non-transitory computer readable medium, may be configured to control a processor to perform a process comprising the example embodiments described above and any combination thereof.

[0093] In an example embodiment, an apparatus, such as, for example, an NFc, NFp or authorization server, or a device controlling functioning thereof, may comprise at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform the example embodiments described above and any combination thereof.

[0094] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more example embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of example embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0095] While the forgoing examples are illustrative of the principles of the example embodiments in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation may be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0096] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY

[0097] At least some example embodiments find industrial application at least in 5G core networks, wherein it is desirable to authorize subscription requests, and possibly in other core networks in the future as well. ACRONYMS LIST

3 GPP 3rd Generation Partnership Project

AEF Application Exposure Function

AF Application Function

AMF Access and Mobility Function

API Application Programming Interfaces

AUSF Authentication Server Function

CAPIF Common API Framework

DRA Diameter Routing Agent

EPC Evolved Packet Core

HSS Home Subscriber Service

IPX IP exchanges

KPI Key Performance Indicator

NEF Network Exposure Function

NF Network Function

NFC NF Consumer

NFP NF Producer

NRF Network Repository Function

NSSF Network Slice Selection Function

NWDAF Network Data Analysis Function

OAM Operations Administration and Maintenance

PCF Policy Control Function

PKI Public Key Infrastructure

PFMN Public Fand Mobile Network

QoS Quality of Service

SBA Service-Based Architecture

SBI Service-Based Interface

SCP Service Communication Proxy

SEPP Security Edge Protection Proxy

SMF Session Management Function

TFS Transport Fayer Security

UDM Unified Data Management UDR User Data Repository

VNF Virtual Network Function

REFERENCE SIGNS LIST