The "AssertionConsumerServiceURL" Placeholder in the SAML Request Template Appear Blank at Login
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Overview
When configuring Auth0 as a SAML Service Provider, a placeholder can be used for AssertionConsumerServiceURL using the @@variableName@@ syntax during the process of customizing the request template. Instead of successfully passing the variable, the value of AssertionConsumerServiceURL returns blank during authentication requests. This article explains why the template variable is not being passed successfully.
Applies To
- SAML Request Template
- AssertionConsumerServiceURL Placeholder
Cause
Variables can be placed into the AuthnRequest template using the @@VariableName@@ syntax.
However, in some circumstances, the AssertionConsumerServiceURL placeholder variable may be empty following an authentication attempt.
Solution
Whether the AssertionConsumerServiceURL placeholder value is expanded at runtime depends on whether or not it was chosen to sign SAML requests.
There are two possible options:
- If requests are not signed, the only acceptable AssertionConsumerService URLs are the ones that have previously been shared with the Identity Provider (IdP) when the trust relationship was established. This means that there is no point in sending this URL in the SAML request.
- If requests are signed, then the IdP can verify the request was not tampered with and trust the ACS URL sent by the Service Provider (SP) in the SAML request.
