title: Invalid request, missing parameter username after keycloak saml login
body: <p>I am using keycloak as an identity broker to a simplesamlphp identity provider in order to login to an angular application.</p>
  
  <p>The keycloak redirects correctly to the identity provider with the login mask. After the login the identity provider redirects as expected to keycloak. Unfortunately I get the following error message (as JSON):</p>
  
  <pre><code>{"error":"invalid_request","error_description":"Missing parameter: username"}
  </code></pre>
  
  <p>My IdP has a user, my keycloak does not, since I do not want to store the users additionally in keycloak.</p>
  
  <p>My broker configuration looks like this:
  <a href="https://i.stack.imgur.com/gfb0f.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gfb0f.png" alt="enter image description here"></a></p>
  
  <p>My client configuration is this:
  <a href="https://i.stack.imgur.com/gcpSV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gcpSV.png" alt="enter image description here"></a></p>
  
  <p>I am familiar with neither SAML nor Keycloak, so if I need to provide any other information, please tell me. </p>