is it fine to pass auth token from one domain to another?

Hi, I have two domains setup. Domain1 has user auth setup with login form.I have a redirect from domain1 to domain2. I want the user auth to be maintained from domain1 to domain2
Also I have logout functionality on both domains which should work for both at a time.
I can't use SSO currently, any other way except SSO i can implement?

I am thinking of passing auth token through url parameter but wanted to know more safer appraoch.
Thanks!!