A computer implemented method performed by a common application program interface, API, framework, CAPIF, core function entity in a communication network, the method comprising: receiving, by the CAPIF core function entity , a registration request from an API management function entity , wherein the registration request includes: security information for CAPIF core function to validate the registration request, and a list of API provider domain functions, which require registration on the CAPIF core function entity ; validating, by the CAPIF core function entity , the registration request; generating, by the CAPIF core function entity , identity and other security-related information for all API provider domain functions in the list of API provider domain functions; and transmitting, by the CAPIF core function entity , the identity and other security-related information in a registration response to the API management function entity , wherein the registration response includes a list of identities for each successfully registered API provider domain function, and wherein, for each API provider domain function in the list of API provider domain functions, the registration response further includes: in response to a successful registration, security information to be used by a successfully registered API provider domain function in subsequent CAPIF API invocations; or in response to a failed registration, reason information related to a registration failure specific to an individual registration-failed API provider domain function. receiving, by the CAPIF core function entity , a registration request from an API management function entity , wherein the registration request includes: security information for CAPIF core function to validate the registration request, and a list of API provider domain functions, which require registration on the CAPIF core function entity ; security information for CAPIF core function to validate the registration request, and a list of API provider domain functions, which require registration on the CAPIF core function entity ; validating, by the CAPIF core function entity , the registration request; generating, by the CAPIF core function entity , identity and other security-related information for all API provider domain functions in the list of API provider domain functions; and transmitting, by the CAPIF core function entity , the identity and other security-related information in a registration response to the API management function entity , wherein the registration response includes a list of identities for each successfully registered API provider domain function, and wherein, for each API provider domain function in the list of API provider domain functions, the registration response further includes: in response to a successful registration, security information to be used by a successfully registered API provider domain function in subsequent CAPIF API invocations; or in response to a failed registration, reason information related to a registration failure specific to an individual registration-failed API provider domain function. in response to a successful registration, security information to be used by a successfully registered API provider domain function in subsequent CAPIF API invocations; or in response to a failed registration, reason information related to a registration failure specific to an individual registration-failed API provider domain function. <EOS>