Function try_extract_otp 

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

Attempt to extract and validate HTTP Basic (OTP) credentials.

Returns:

• Some(Ok(AuthResult)) — valid OTP, authentication succeeded
• Some(Err(Response)) — credentials present but invalid (401)
• None — no HTTP Basic header present (try next auth method)