diff --git a/src/saml.ts b/src/saml.ts
index f821216..d2fbb5a 100644
--- a/src/saml.ts
+++ b/src/saml.ts
@@ -1,5 +1,7 @@
 import { SAML, SamlConfig } from '@node-saml/node-saml';
-import { signAuthnRequestPost } from '@node-saml/node-saml/lib/saml-post-signing';
+// import { signAuthnRequestPost } from '@node-saml/node-saml/lib/saml-post-signing';
+import { signAuthRequest } from './signAuthRequest';
+
 import { SpidRequest } from './request';
 import { SamlSpidProfile, SpidConfig } from './types';
 import { SpidResponse } from './response';
@@ -31,7 +33,18 @@ export class SpidSAML extends SAML {
     xml = req.generate(this.options).xml();
     if (this.options.authnRequestBinding === 'HTTP-POST') {
       // re-sign request
-      xml = signAuthnRequestPost(xml, this.options as any);
+         //xml = signAuthnRequestPost(xml, this.options as any);
+
+        const { spid, saml } = this.spidConfig;
+        const { privateKey, signatureAlgorithm } = saml;
+        const cert = spid.serviceProvider.certificate;
+        xml = signAuthRequest(xml, {
+          signatureAlgorithm: signatureAlgorithm,
+          privateKey,
+          certificate: cert,
+          action: 'after',
+          nodeName: 'AuthnRequest',
+        });
     }
     const { cache } = this.spidConfig;
     const cacheData: CacheData = {
diff --git a/src/signAuthRequest.ts b/src/signAuthRequest.ts
new file mode 100644
index 0000000..e7ef8e5
--- /dev/null
+++ b/src/signAuthRequest.ts
@@ -0,0 +1,42 @@
+import { SignedXml } from 'xml-crypto';
+
+const authnRequestXPath =
+  '/*[local-name(.)="AuthnRequest" and namespace-uri(.)="urn:oasis:names:tc:SAML:2.0:protocol"]';
+const issuerXPath =
+  '/*[local-name(.)="Issuer" and namespace-uri(.)="urn:oasis:names:tc:SAML:2.0:assertion"]';
+
+export const signAuthRequest = (
+  xml: string,
+  options: {
+    privateKey: string | Buffer;
+    signatureAlgorithm: string;
+    nodeName: string;
+    certificate?: string;
+    action?: 'prepend' | 'append' | 'after';
+  },
+) => {
+  const { privateKey, signatureAlgorithm, nodeName, certificate, action } =
+    options;
+  const sig = new SignedXml();
+  sig.signingKey = privateKey;
+  if (certificate)
+    sig.keyInfoProvider = {
+      file: '',
+      getKey: () => Buffer.from(privateKey),
+      getKeyInfo: () =>
+        `<X509Data><X509Certificate>${certificate}</X509Certificate></X509Data>`,
+    };
+  sig.signatureAlgorithm = `http://www.w3.org/2001/04/xmldsig-more#rsa-${signatureAlgorithm}`;
+  sig.addReference(
+    `//*[local-name(.)='${nodeName}']`,
+    [
+      'http://www.w3.org/2000/09/xmldsig#enveloped-signature',
+      'http://www.w3.org/2001/10/xml-exc-c14n#',
+    ],
+    `http://www.w3.org/2001/04/xmlenc#${signatureAlgorithm}`,
+  );
+  sig.computeSignature(xml, {
+    location: { reference: authnRequestXPath + issuerXPath, action: 'after' },
+  });
+  return sig.getSignedXml();
+};