According to an example aspect of the present invention, there is provided a method comprising, receiving, by an intermediary network function, a subscription request from a network function consumer requesting data of a network function producer, wherein the subscription request comprises a client credential assertion of the network function consumer and an access token, authorizing and authenticating, by the intermediary network function, the network function consumer upon successful validation of the access token and the client credential assertion validation and transmitting, by the intermediary network function, an access token request to an authorization server to get another access token, wherein said another access token is to be used to validate the network function consumer to access services of the network function producer, and the access token request comprises the client credential assertion of the network function consumer requesting data of the network function producer.