public SamlIdentityProviderConfigBuilder idp() {
        final SamlIdentityProviderConfigBuilder config = new SamlIdentityProviderConfigBuilder(this);
        idpConfigBuilders.add(config);
        return config;
    }
Returns a {@link SamlIdentityProviderConfigBuilder} to configure a new idp for authentication.
saml/src/main/java/com/linecorp/armeria/server/saml/SamlServiceProviderBuilder.java