Document identity verification exemptions

doc/security/identity_verification.md

@@ -20,6 +20,8 @@ three stages of verification to register an account:
 - **Medium-risk users** - Phone number verification.
 - **High-risk users** - Credit card verification.
 
+Users created after signing in with [SAML SSO for GitLab.com groups](../user/group/saml_sso/index.md) are exempt from identity verification.
+
 ## Email verification
 
 To register an account, you must provide a valid email address.