How to implement ClientCertVerifier trait of rustTls

I tried to implement the trait ClientCertVerifier, I need the method that check the client certificate the problem is when I write this block of code

impl ClientCertVerifier for rustls::NoClientAuth {
    fn verify_client_cert(


        presented_certs: &[Certificate],

        sni: Option<&DNSName>,

    ) -> Result<ClientCertVerified, TLSError> {
        // My code to check the ceritificate


I get this error :

conflicting implementations of trait rustls::ClientCertVerifier for type rustls::NoClientAuth:
conflicting implementation in crate rustls:

  • impl ClientCertVerifier for NoClientAuth;

What I'm doing wrong ?

What's the problem you're trying to solve by writing this impl? You can't implement a trait for a type when both of them are defined outside the current crate, and anyway rustls::NoClientAuth already implements rustls::ClientCertVerifier, so this shouldn't be necessary.

If you want to define your own checking behavior you could define your own type MyClientAuth and then impl ClientCertVerifier for MyClientAuth. I can't say for certain whether that's the right thing to do here because I'm not familiar with rustls or what you're trying to do in your custom checking logic.