Keyclock gitlab saml connect 500 error,help

Keycloak configures LDAP to provide user data, and adds gitlab configuration in client, as shown in the figure .

gitlab.rb configure

After clicking gitlab SAML keyclock and logging in with LDAP user name and password, the following error is reported.
Google browser checks post error 500,

gitlab-ctl tail, Don’t know what reason, but also trouble the God of the community to help see, thank you!