Add Self-Signed Certificate Mutual-TLS client authentication method #1559
Description
Add support for Self-Signed Certificate Mutual-TLS client authentication method (self_signed_tls_client_auth).
See section 2.2. Self-Signed Certificate Mutual-TLS Method in RFC 8705 OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens.
Related gh-101