If you are running your portal to host your blog like I am then you might want to get rid of some of the login options on the sign in page.
In my case, the only option for sign in that I want is Azure AD.

The available options on the sign in page are:
  • Local SignIn - this is using credentials stored in Common Data Service / CDS on a contact record
  • Register - this allows users to register a new user account (contact record) in CDS
  • Redeem invitation - this allows users to register using an invitation code generated in CDS and usually sent to user via email.
  • External SignIn - this options use Azure AD credentials for signing in to the portal.

original signin page

Here are the steps to remove the obsolete sign in options
  1. Go to Site Settings in PowerApps Portal Management
     
  2. Select the settings to edit by click in the very left column of the relevant records.
    I have change the following settings:
    - Authentication/Registration/Enabled
    - Authentication/Registration/ExternalLoginEnabled
    - Authentication/Registration/InvitationEnabled
    - Authentication/Registration/LocalLoginEnabled


    Edit the site settings for authentication
     
  3. Click Edit to edit multiple records at once.
     
  4. type false in the Value field and click the Change button

    Edit multiple records
     
  5. Done
     
Browsing to the sign in page shows the simple form with only Azure AD signin available

Customized signin page
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