Information
A SAML (Security Assertions Markup Language) authentication assertion is issued as proof of an authentication event and can be signed.
WebSphere Liberty should require that SAML assertions ( <saml:Assertion> elements) contain a signature element that signs the assertion so that it can be verified securely by the server.
Solution
Add the wantAssertionsSigned attribute to all samlWebSso20 elements to ${server.config.dir}/configDropins/overrides/*.xml and set it to true
<samlWebSso20 ...
wantAssertionsSigned="true"
/>