Azure AD B2C using b2clogin.com domain

Does anyone have pointers on getting an Azure AD B2C auth provider set up to use the <tenant>.b2clogin.com address instead of login.microsoftonline.com?

I'm using the Open ID Connect provider type, and if I set it up with the login.microsoft.com endpoint URLs, I can get a successful test with the test-only initialization URL. 

If I set the endpoint URLs to use the endpoints for the b2clogin.com domain, I keep getting No_Oauth_Token: Access token was not returned. 

These endpoints work:

Authorize: https://login.microsoftonline.com/<tenant>/oauth2/authorize

Token:

https://login.microsoftonline.com/<tenant>/oauth2/token

These endpoints give No_Oauth_Token:

Authorize:

https://<tenant>.b2clogin.com/<tenant>/oauth2/v2.0/authorize?p=<standard signup and signin user flow>

Token:

https://<tenant>.b2clogin.com/<tenant>/oauth2/v2.0/token?p=<standard signup and signin user flow>

Thanks!