Cannot get access token using tls_client_auth

[benjefferies]

Describe the bug When trying to get an access token using tls_client_auth I get the error

curl --location --request POST 'https://matls.as.aspsp.ob.forgerock.financial/oauth2/access_token' \
--header 'Content-Type: application/x-www-form-urlencoded' \
--data-urlencode 'grant_type=client_credentials' \
--data-urlencode 'scope=openid accounts' \
--data-urlencode 'client_id=ad5fc2de-aa11-4b2f-aa66-615e8a388169'
{"error_description":"Invalid authentication method for accessing this endpoint.","error":"invalid_client"}

To Reproduce Steps to reproduce the behaviour:

1. Dynamically register with the token_endpoint_auth_method and tls_client_auth_subject_dn

     "token_endpoint_auth_method": "tls_client_auth",
     "tls_client_auth_subject_dn": "YOUR SUBJECT DN",

2. Try to get an access token

   curl --location --request POST 'https://matls.as.aspsp.ob.forgerock.financial/oauth2/access_token' \
   --header 'Content-Type: application/x-www-form-urlencoded' \
   --data-urlencode 'grant_type=client_credentials' \
   --data-urlencode 'scope=openid accounts' \
   --data-urlencode 'client_id=ad5fc2de-aa11-4b2f-aa66-615e8a388169'

Expected behaviour An access token

Current behaviour

{"error_description":"Invalid authentication method for accessing this endpoint.","error":"invalid_client"}

[benjefferies]

Fixed and tested in integration environment