We prefer one that doesn't try to store employee creds, and lets only current employees use the service seamlessly.

As a small business (< 100 devs), we happily allow SaaS tools but only if the tool supports OIDC ("Continue with" or "Sign in with" buttons) for a domain, or SAML (traditional SSO).

The OIDC/Oauth2 path is straightforward to implement then "no brainer" for new sign-ups (no SSO support nightmare). If tied together with a domain name match supports it is good enough for almost every U.S. small to mid business, from tens to thousands of employees, even regulated businesses.

Letting even a one person company control access to services the company uses is not "enterprise", it's just security matters 101.

I strongly prefer open source, but am certainly not opposed to closed source and will use that if it solves the problem better enough to overcome the fact that it's not open source.