[Accelerator 4] Access token attributes cannot be added from IS console UI

[imesh94]

We have written FSDefaultOIDCClaimsCallbackHandler [1] extending DefaultOIDCClaimsCallbackHandler to add consent_id as a jwt access token claim. To engage this, we are setting enable_claims_separation_for_access_tokens = false in IS deployment.toml.

However, this overrides the default behavior in IS, because

1. Access token claims cannot be added when enable_claims_separation_for_access_tokens is set to false. This is due to the logic at [2], where this configuration is checked before updating the access token claims.

2. When enable_claims_separation_for_access_tokensis set to false, IS defaultJWTAccessTokenOIDCClaimsHandler` is not engaged. This is due to the logic at [3], where it decides which claims handler to engaged based on the config.

Proposed Solution: Instead of using FSDefaultOIDCClaimsCallbackHandler, a JWTAccessTokenClaimProvider [4] can be added to set consent_id as a jwt access token claim. If we follow this approach, there is no need to set `enable_claims_separation_for_access_tokens' as false, and IS default behavior will be preserved.

OB Internal Ticket: https://github.com/wso2-enterprise/wso2-ob-internal/issues/1281

[1] - https://github.com/wso2/financial-services-accelerator/blob/v4.1.1/financial-services-accelerator/components/org.wso2.financial.services.accelerator.identity.extensions/src/main/java/org/wso2/financial/services/accelerator/identity/extensions/claims/FSDefaultOIDCClaimsCallbackHandler.java

[2] - https://github.com/wso2-extensions/identity-inbound-auth-oauth/blob/v7.1.10/components/org.wso2.carbon.identity.oauth/src/main/java/org/wso2/carbon/identity/oauth/OAuthAdminServiceImpl.java#L1014

[3] - https://github.com/wso2-extensions/identity-inbound-auth-oauth/blob/v7.1.10/components/org.wso2.carbon.identity.oauth/src/main/java/org/wso2/carbon/identity/openidconnect/util/ClaimHandlerUtil.java#L51

[4] - https://github.com/wso2-extensions/identity-inbound-auth-oauth/blob/v7.1.10/components/org.wso2.carbon.identity.oauth/src/main/java/org/wso2/carbon/identity/oauth2/token/handlers/claims/JWTAccessTokenClaimProvider.java