@UnstableApi
    public ClientFactoryBuilder tlsProvider(TlsProvider tlsProvider) {
        requireNonNull(tlsProvider, "tlsProvider");
        checkState(!staticTlsSettingsSet,
                   "Cannot configure the TlsProvider because static TLS settings have been set already.");
        this.tlsProvider = tlsProvider;
        tlsConfig = null;
        return this;
    }
Sets the {@link TlsProvider} that provides {@link TlsKeyPair}s for client certificate authentication.
<pre>
ClientFactory
  .builder()
  .tlsProvider(
    TlsProvider.builder()
               // Set the default key pair.
               .keyPair(TlsKeyPair.of(...))
               // Set the key pair for "example.com".
               .keyPair("example.com", TlsKeyPair.of(...))
               .build())
</pre>
core/src/main/java/com/linecorp/armeria/client/ClientFactoryBuilder.java