SAML authentication

When you setup SAML access you need to provide a correct callback URL. According to what you are saying the callback URL is incorrect. The manual explains what kind of the URL you need to use:
https://xlinesoft.com/phprunner/docs/saml_authentication.htm

My provider is google. when I configure the parameters in my goggle admin console, I have to insert URL ACS and Identity ID. Looking on internet I've read that the URL ACS is the url of my application comprensive of samlcallback.php e.g. https://mysite.com/myapp/samlcallback.php, it's corretct? Where I find the Identity ID? in other configurations I've used an arbitrary Identity ID, and I've insert it both in google admin console and in 3th part application. How I can do it with phprunner? Where I've to input the Identity ID in my PHPR application. Here there are all informations relative to the application. Application URL: https://mydomain.com/todo_app; entityID from google metadata: entityID="https://accounts.google.com/o/saml2?idpid=xxxxxxxx; SingleSignOnService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Redirect" Location="https://accounts.google.com/o/saml2/idp?idpid=xxxxxxxx"/>'>https://accounts.google.com/o/saml2/idp?idpid=xxxxxxxx"/>; <md:SingleSignOnService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST" Location="https://accounts.google.com/o/saml2/idp?idpid=xxxxxxxx"/>'>https://accounts.google.com/o/saml2/idp?idpid=xxxxxxxx"/>;.
If is usefull here there is the samlcallback.php file.

The indications of the manual are not clear for me.

This is the error on browser when try to authenticate:
400. That’s an error.
The server cannot process the request because it is malformed. It should not be retried. That’s all we know.

I'm desperated.

Please help me.

This doesn't make any sense to me. I guess you need to contact support directly senfding screenshots of your SAML setup in Google.