You can use your Google credentials to sign in to HackerOne. To set up SSO via SAML for Google:
Log in to the G Suite Admin Console.
Click SAML apps.
Click on the '+' in the bottom right hand corner to enable SSO for a SAML application.
Find and click on HackerOne in the Apps list.
Copy the SSO URL and Certificate.
Click Next on the Basic Information for HackerOne window
Click Next on the Service Provider Details window
Adjust the attribute mapping as needed.
Click OK to confirm.
Click Edit Service.
Edit the options to enroll users or organizational units into the HackerOne application. The status will change stating that the application is ON.
Follow the SAML setup instructions here.
Paste the Single-Sign On URL and the X.509 Certificate that you copied from step 6 into the corresponding fields during SAML setup.