Function try_extract_gssapi 

pub async fn try_extract_gssapi(
    parts: &mut Parts,
    app: &Arc<AppState>,
) -> Option<Result<AuthResult, Response>>

Attempt to extract and validate GSSAPI/SPNEGO credentials.

Returns:

• Some(Ok(AuthResult)) — GSSAPI authentication succeeded
• Some(Err(Response)) — Negotiate header present but invalid (401/403)
• None — no Negotiate header present (try next auth method)