public SamlServiceProviderBuilder ssoHandler(SamlSingleSignOnHandler ssoHandler) {
        this.ssoHandler = requireNonNull(ssoHandler, "ssoHandler");
        return this;
    }
Sets a {@link SamlSingleSignOnHandler} which handles SAML messages for a single sign-on.
saml/src/main/java/com/linecorp/armeria/server/saml/SamlServiceProviderBuilder.java