title: SAML Attribute Mapping for Aws Cognito - Signup or Signin works but not both
body: <p>I have setup my GSuite account as a SAML iDP for Cognito User Pools (not identity pools).</p>
  
  <p>If i provide no attribute mappings a new user trying to signup via GSuite login gets the following error.</p>
  
  <blockquote>
    <p>Error in SAML response processing: Invalid user attributes: email: Attribute is required.</p>
  </blockquote>
  
  <p>However if I add an email mapping, the user can signup. But can't ever sign in again as they get this error (strange as email is writable by this app client)</p>
  
  <blockquote>
    <p>Error in SAML response processing: Invalid user attributes: email: Attribute cannot be updated.</p>
  </blockquote>
  
  <p>Ideas as to whats going on?</p>
  
  <p>In browser, using Hosted UI.</p>