diff --git a/CHANGELOG b/CHANGELOG
index a25edfb..6a8a2f8 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,9 @@
 # Changelog
 
+### Unreleased
+
+- Add `signed_post` function to `AuthnRequest`
+
 ### 0.0.15
 
 - Updates dependencies
diff --git a/src/idp/response_builder.rs b/src/idp/response_builder.rs
index c5ac56e..db657e7 100644
--- a/src/idp/response_builder.rs
+++ b/src/idp/response_builder.rs
@@ -124,7 +124,7 @@ fn build_response(
         destination: Some(destination.to_string()),
         consent: None,
         issuer: Some(issuer.clone()),
-        signature: Some(Signature::template(&response_id, x509_cert)),
+        signature: Some(Signature::default_template(&response_id, x509_cert)),
         status: Some(Status {
             status_code: StatusCode {
                 value: Some("urn:oasis:names:tc:SAML:2.0:status:Success".to_string()),
diff --git a/src/schema/authn_request.rs b/src/schema/authn_request.rs
index f7e670b..19b39bb 100644
--- a/src/schema/authn_request.rs
+++ b/src/schema/authn_request.rs
@@ -121,6 +121,29 @@ impl AuthnRequest {
         self
     }
 
+    pub fn add_signature(&mut self, signature: Signature) -> &mut Self {
+        self.signature = Some(signature);
+        self
+    }
+
+    pub fn default_signature(&mut self, certificate_der: &[u8]) -> &mut Self {
+        self.add_signature(Signature::default_template(&self.id, certificate_der))
+    }
+
+    pub fn make_signature(
+        &mut self,
+        certificate_der: &[u8],
+        sig_alg: &str,
+        digest_alg: &str,
+    ) -> &mut Self {
+        self.add_signature(Signature::template(
+            &self.id,
+            certificate_der,
+            sig_alg,
+            digest_alg,
+        ))
+    }
+
     #[cfg(feature = "xmlsec")]
     pub fn to_signed_xml(
         &self,
diff --git a/src/service_provider/mod.rs b/src/service_provider/mod.rs
index a237052..a0a41a6 100644
--- a/src/service_provider/mod.rs
+++ b/src/service_provider/mod.rs
@@ -78,6 +78,8 @@ pub enum Error {
     ResponseExpired { time: String },
     #[error("SAML Response StatusCode is not successful: {}", code)]
     ResponseBadStatusCode { code: String },
+    #[error("Failed to sign AuthnRequest: Signature is missing")]
+    RequestMissingSignature,
     #[error("Encrypted SAML Assertions are not yet supported")]
     EncryptedAssertionsNotYetSupported,
     #[error("SAML Response and all assertions must be signed")]
@@ -512,9 +514,26 @@ fn parse_certificates(key_descriptor: &KeyDescriptor) -> Result<Vec<x509::X509>,
 
 impl AuthnRequest {
     pub fn post(&self, relay_state: &str) -> Result<Option<String>, Box<dyn std::error::Error>> {
-        let encoded = general_purpose::STANDARD.encode(self.to_xml()?.as_bytes());
+        Ok(self.make_post(&self.to_xml()?, relay_state))
+    }
+
+    pub fn signed_post(
+        &self,
+        relay_state: &str,
+        private_key_der: &[u8],
+    ) -> Result<Option<String>, Box<dyn std::error::Error>> {
+        if self.signature.is_none() {
+            Err(Error::RequestMissingSignature)?
+        }
+
+        let signed_request = crypto::sign_xml(&self.to_xml()?, &private_key_der)?;
+        Ok(self.make_post(&signed_request, relay_state))
+    }
+
+    fn make_post(&self, request: &str, relay_state: &str) -> Option<String> {
+        let encoded = general_purpose::STANDARD.encode(request.as_bytes());
         if let Some(dest) = &self.destination {
-            Ok(Some(format!(
+            Some(format!(
                 r#"
             <form method="post" action="{}" id="SAMLRequestForm">
                 <input type="hidden" name="SAMLRequest" value="{}" />
@@ -527,9 +546,9 @@ impl AuthnRequest {
             </script>
         "#,
                 dest, encoded, relay_state
-            )))
+            ))
         } else {
-            Ok(None)
+            None
         }
     }
 
diff --git a/src/signature.rs b/src/signature.rs
index 2878fa6..58bcabc 100644
--- a/src/signature.rs
+++ b/src/signature.rs
@@ -21,7 +21,16 @@ pub struct Signature {
 }
 
 impl Signature {
-    pub fn template(ref_id: &str, x509_cert_der: &[u8]) -> Self {
+    pub fn default_template(ref_id: &str, x509_cert_der: &[u8]) -> Self {
+        Signature::template(
+            ref_id,
+            x509_cert_der,
+            "http://www.w3.org/2001/04/xmldsig-more#rsa-sha256",
+            "http://www.w3.org/2000/09/xmldsig#sha1",
+        )
+    }
+
+    pub fn template(ref_id: &str, x509_cert_der: &[u8], sig_alg: &str, digest_alg: &str) -> Self {
         Signature {
             id: None,
             signed_info: SignedInfo {
@@ -30,7 +39,7 @@ impl Signature {
                     algorithm: "http://www.w3.org/2001/10/xml-exc-c14n#".to_string(),
                 },
                 signature_method: SignatureMethod {
-                    algorithm: "http://www.w3.org/2001/04/xmldsig-more#rsa-sha256".to_string(),
+                    algorithm: sig_alg.to_string(),
                     hmac_output_length: None,
                 },
                 reference: vec![Reference {
@@ -48,7 +57,7 @@ impl Signature {
                         ],
                     }),
                     digest_method: DigestMethod {
-                        algorithm: "http://www.w3.org/2000/09/xmldsig#sha1".to_string(),
+                        algorithm: digest_alg.to_string(),
                     },
                     digest_value: Some(DigestValue {
                         base64_content: Some("".to_string()),