How the IdP know the name of the variable that contain the authnRequest

Question

I implement an saml identity provider, The servise provider send an HTML from that containt the authnRequest in an hide input, that have a name for example SAMLRequest.

<form id="samlRequestId" action="http://localhost:8084/IdentityProvider/SSOService" method="post">
  <input type="hidden" name="RelayState" value="token" />
  <input type="hidden" name="SAMLRequest" value="samlRequestValue"</input> 
</form>

But how the IdP know this name(SAMLRquest), actually I hard coded this name, I ask if there are any other method?

Answer 1

The attribute name "SAMLRequest" is defined as part of the SAML 2.0 standard. You can find more details about it in http://docs.oasis-open.org/security/saml/v2.0/saml-bindings-2.0-os.pdf, it's in chapter 3.4 HTTP Redirect Binding.