The question was answered many times already but I am looking a way to customise login screen for multi-tenant web applications registered in Azure AD the way https://portal.azure.com does.
I am aware about custom login page for b2c apps documented at https://docs.microsoft.com/en-us/azure/active-directory-b2c/customize-ui-overview and company branding documented at https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/customize-branding. The former uses b2clogin.com domain and an option to use MSA as external ID provider. The later applies branding of user's tenant and on the password prompt only.
portal.azure.com instead looks like a mix of both. It uses regular OpenId Connect v1 endpoints and redirects to
https://login.microsoftonline.com/common/oauth2/authorize
?resource=https%3a%2f%2fmanagement.core.windows.net%2f
&response_mode=form_post
&response_type=code+id_token
&scope=user_impersonation+openid
&client_id=c44b4083-3bb0-49c1-b47d-974e53cbdf3c
&redirect_uri=https%3a%2f%2fportal.azure.com%2fsignin%2findex%2f%3ffeature.refreshtokenbinding%3dtrue
The login prompt however presents application logo and github login option similarly to b2c but allows to use MSA account like usual login.microsoftonline.com:
I am wondering if it is possible to do something similar for my own app. The similar question Custom Branding for Login on a Azure AD Multi-Tenant App was asked a few years ago, and the only answer there suggests it's a feature of Microsoft owned apps. Even tho the answer was not accepted I'd trust Anton on this account. Is it still the case today?