要解决"AuthnRequest未被签名"的问题，你需要对AuthnRequest进行签名。下面是一个使用Java和OpenSAML库的示例代码，用于创建和签名一个AuthnRequest。

首先，确保你已经在项目中添加了OpenSAML依赖。你可以在Maven项目中添加以下依赖项：

    org.opensaml
    opensaml-core
    3.4.1


    org.opensaml
    opensaml-saml-api
    3.4.1


    org.opensaml
    opensaml-saml-impl
    3.4.1

接下来，你可以使用以下代码创建和签名一个AuthnRequest：

import org.joda.time.DateTime;
import org.opensaml.core.config.Configuration;
import org.opensaml.core.config.InitializationService;
import org.opensaml.core.xml.io.MarshallingException;
import org.opensaml.saml.common.SAMLObjectBuilder;
import org.opensaml.saml.common.xml.SAMLConstants;
import org.opensaml.saml.saml2.core.AuthnContextClassRef;
import org.opensaml.saml.saml2.core.AuthnRequest;
import org.opensaml.saml.saml2.core.Issuer;
import org.opensaml.security.SecurityException;
import org.opensaml.xmlsec.SignatureSigningConfiguration;
import org.opensaml.xmlsec.SignatureSigningParameters;
import org.opensaml.xmlsec.config.DefaultSecurityConfigurationBootstrap;
import org.opensaml.xmlsec.keyinfo.KeyInfoGenerator;
import org.opensaml.xmlsec.keyinfo.KeyInfoGeneratorFactory;
import org.opensaml.xmlsec.keyinfo.KeyInfoGeneratorManager;
import org.opensaml.xmlsec.keyinfo.NamedKeyInfoGeneratorManager;
import org.opensaml.xmlsec.signature.KeyInfo;
import org.opensaml.xmlsec.signature.KeyInfoGeneratorManagerFactory;
import org.opensaml.xmlsec.signature.Signature;
import org.opensaml.xmlsec.signature.support.SignatureConstants;
import org.opensaml.xmlsec.signature.support.Signer;

import javax.xml.namespace.QName;

public class AuthnRequestSigner {

    public static void main(String[] args) throws Exception {
        // 初始化OpenSAML配置
        InitializationService.initialize();

        // 创建AuthnRequest对象
        AuthnRequest authnRequest = createAuthnRequest();

        // 对AuthnRequest进行签名
        signAuthnRequest(authnRequest);

        // 输出签名后的AuthnRequest
        System.out.println(XMLUtils.marshall(authnRequest));
    }

    private static AuthnRequest createAuthnRequest() {
        // 创建SAML对象构建器
        SAMLObjectBuilder authnRequestBuilder = (SAMLObjectBuilder) Configuration.getBuilderFactory().getBuilder(AuthnRequest.DEFAULT_ELEMENT_NAME);
        SAMLObjectBuilder issuerBuilder = (SAMLObjectBuilder) Configuration.getBuilderFactory().getBuilder(Issuer.DEFAULT_ELEMENT_NAME);
        SAMLObjectBuilder authnContextClassRefBuilder = (SAMLObjectBuilder) Configuration.getBuilderFactory().getBuilder(AuthnContextClassRef.DEFAULT_ELEMENT_NAME);

        // 创建AuthnRequest对象
        AuthnRequest authnRequest = authnRequestBuilder.buildObject();
        authnRequest.setID("_" + String.valueOf(new DateTime().getMillis()));
        authnRequest.setVersion(SAMLVersion.VERSION_2_0);
        authnRequest.setIssueInstant(new DateTime());
        authnRequest.setDestination("https://example.com/destination");
        authnRequest.setProtocolBinding(SAMLConstants.SAML2_POST_BINDING_URI);

        // 设置Issuer
        Issuer issuer = issuerBuilder.buildObject();
        issuer.setValue("https://example.com/issuer");
        authnRequest.setIssuer(issuer);

        // 设置AuthnContextClassRef
        AuthnContextClassRef authnContextClassRef = authnContextClassRefBuilder.buildObject();
        authnContextClassRef.setAuthnContextClassRef(AuthnContext.PASSWORD_AUTHN_CTX);
        authnRequest.setRequestedAuthnContext(authnContextClassRef);

        return authnRequest;
    }

    private static void signAuthnRequest(AuthnRequest authnRequest) throws SecurityException, MarshallingException {
        // 获取默认的签名配置
        SignatureSigningConfiguration signingConfig = DefaultSecurityConfigurationBootstrap.buildDefaultSignatureSigningConfiguration();

        // 创建签名参数