Implement signed AuthnRequests

Author: John Lynch

README.md

@@ -22,6 +22,27 @@ redirect_to saml_request.url(
 )
 ```
 
+### Initiating a signed authentication request
+
+The signed SAML request must have a Destination node, specified as `destination_url`
+
+```ruby
+saml_request = Samlr::Request.new(
+  :issuer               => request.host,
+  :name_identity_format => Samlr::EMAIL_FORMAT,
+  :consumer_service_url => "https://#{request.host}/auth/saml",
+  :sign_requests => true,
+  :destination_url => "https://adfs.company.com/adfs/ls/",
+  :signing_certificate => Samlr::Tools::CertificateBuilder.read(private_key_pem, certifictate_pem)
+)
+```
+This will sign the URL with your private key and look something like this:
+
+```
+https://foo.com/?SAMLRequest=...Base64 Encoded SAML Request...&SigAlg=http%3A%2F%2Fwww.w3.org%2F2000%2F09%2Fxmldsig%23rsa-sha1&Signature=tvY57vi6IXHP1gHAMRQoRP5CZQlUniPwSeuwOUypqbjim04svTkk72njvbxzUE27U5PhK0Cwzq4ZdZ08i%2BuVAw%3D%3D
+```
+
+
 Once the IdP receives the request, it prompts the user to authenticate, after which it sends the SAML response to your application.
 
 ### Verifying a SAML response

lib/samlr/request.rb

@@ -20,18 +20,35 @@ def body
 
     # Utility method to get the full redirect destination, Request#url("https://idp.example.com/saml", { :RelayState => "https://sp.example.com/saml" })
     def url(root, params = {})
-      dest = root.dup
-      if dest.include?("?")
-        dest << "&SAMLRequest=#{param}"
-      else
-        dest << "?SAMLRequest=#{param}"
+      params = params.dup
+      buffer = root.dup
+      buffer << (buffer.include?("?") ? "&" : "?")
+
+      signable = "SAMLRequest=#{param}"
+
+      if params[:RelayState]
+        signable << "&RelayState=#{CGI.escape(params.delete(:RelayState))}"
+      end
+
+      if options[:sign_requests]
+        signable << "&SigAlg=#{CGI.escape('http://www.w3.org/2000/09/xmldsig#rsa-sha1')}"
+        signable << "&Signature=#{CGI.escape(compute_signature(signable))}"
       end
 
+      buffer << signable
+
       params.each_pair do |key, value|
-        dest << "&#{key}=#{CGI.escape(value.to_s)}"
+        buffer << "&#{key}=#{CGI.escape(value.to_s)}"
       end
 
-      dest
+      buffer
+    end
+
+    private
+    def compute_signature(signable)
+      certificate  = options[:signing_certificate]  #instance of Samlr::Tools::CertificateBuilder
+      certificate.sign(signable)
     end
+
   end
 end

lib/samlr/tools/certificate_builder.rb

@@ -69,6 +69,13 @@ def self.load(path, id = "samlr")
 
         new(:key_pair => key_pair, :x509 => x509_cert)
       end
+
+      def self.read(private_key_pem, certificate_pem)
+        key_pair  = OpenSSL::PKey::RSA.new(private_key_pem)
+        x509_cert = OpenSSL::X509::Certificate.new(certificate_pem)
+
+        new(:key_pair => key_pair, :x509 => x509_cert)
+      end
     end
   end
 end

lib/samlr/tools/request_builder.rb

@@ -7,6 +7,7 @@ module Tools
     module RequestBuilder
       def self.build(options = {})
         consumer_service_url = options[:consumer_service_url]
+        destination_url      = options[:destination_url]
         issuer               = options[:issuer]
         name_identity_format = options[:name_identity_format]
         allow_create         = options[:allow_create] || "true"
@@ -20,6 +21,10 @@ def self.build(options = {})
               xml.doc.root["AssertionConsumerServiceURL"] = consumer_service_url
             end
 
+            unless destination_url.nil?
+              xml.doc.root["Destination"] = destination_url
+            end
+
             unless issuer.nil?
               xml["saml"].Issuer(issuer)
             end

test/unit/test_request.rb

@@ -31,4 +31,13 @@
       end
     end
   end
+
+  describe "#signed_url" do
+    let(:signed_request) {Samlr::Request.new(:sign_requests => true, :signing_certificate => TEST_CERTIFICATE)}
+    it "returns a signed URL" do
+      signed_request.stub(:param, "hello") do
+        assert_equal("https://foo.com/?SAMLRequest=hello&SigAlg=http%3A%2F%2Fwww.w3.org%2F2000%2F09%2Fxmldsig%23rsa-sha1&Signature=tvY57vi6IXHP1gHAMRQoRP5CZQlUniPwSeuwOUypqbjim04svTkk72njvbxzUE27U5PhK0Cwzq4ZdZ08i%2BuVAw%3D%3D&foo=bar", signed_request.url("https://foo.com/", :foo => "bar"))
+      end
+    end
+  end
 end