Description

This PR fixes issue #143 where Authelia OIDC login fails due to a missing or weak state parameter.

Changes include:

• Secure State Generation: Generates a cryptographically strong 16-byte random state (base64 encoded) in UserOidcAuth.new/2.
• Nonce Support: Generates a secure nonce for additional security and passes it to Oidcc.
• Validation: Validates the state parameter in UserOidcAuth.callback/2 against the session value to prevent CSRF attacks.
• Tests: Added UserOidcAuthTest to verify the presence of security parameters in the session and proper error handling.

/claim #143