### Summary There is no way currently to pass custom form parameters as part of OAuth2ClientCredentialsGrantRequestEntityConverter: https://github.com/spring-projects/spring-security/blob/master/oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/endpoint/OAuth2ClientCredentialsGrantRequestEntityConverter.java Some IDPs (Auth0 for example) require an "audience" value.
Summary
There is no way currently to pass custom form parameters as part of OAuth2ClientCredentialsGrantRequestEntityConverter:
https://github.com/spring-projects/spring-security/blob/master/oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/endpoint/OAuth2ClientCredentialsGrantRequestEntityConverter.java
Some IDPs (Auth0 for example) require an "audience" value.