You can verify the domains you use for federated sign-in.
You must be a Super Admin.
You need to verify a domain and an identity provider to use federated sign-in. See Set up Federated sign-in.
If you want to use federated sign-in as your sign-in option, you must ensure that all your administrators and users are assigned to a domain and have an identity provider.
You can add up to 20 domains. When you add a domain, you're verifying that you own it. You can only associate a user with one domain.
Click Add domain to start verifying a domain. See Verify a federated domain.
You must verify you own the domains you add. You do this by adding a TXT record to your public-facing DNS. It takes up to 24 hours for the changes to the DNS to propagate. You can then verify the domain. Click Verify domain ownership to do this.
Verified domains show as verified with a date in the list of domains. Verification lasts for a year, and you can re-verify at any point during the year.