code: private String toApacheAuthenticationScheme(ProxyAuthenticationMethod authenticationMethod) {
          if (authenticationMethod == null) {
              throw new IllegalStateException("The configured proxy authentication methods must not be null.");
          }
  
          switch (authenticationMethod) {
              case NTLM: return AuthSchemes.NTLM;
              case BASIC: return AuthSchemes.BASIC;
              case DIGEST: return AuthSchemes.DIGEST;
              case SPNEGO: return AuthSchemes.SPNEGO;
              case KERBEROS: return AuthSchemes.KERBEROS;
              default: throw new IllegalStateException("Unknown authentication scheme: " + authenticationMethod);
          }
      }
docs: Convert the customer-facing authentication method into an apache-specific authentication method.