When sending an OIDC token-request including client-secret (and client-id), the configured client-secret is changed: Any ending = is converted to %3D

To Reproduce
authenticate against an OIDC provider that requires
spring.security.oauth2.client.registration.<provider>.client-authentication-method=client_secret_post
with a client-secret that ends with padding character =

That will result in a token-request where the padding character is replaced by unicode %3D

Expected behavior
padding character for client-id should not be converted to unicode