To allow your WordPress website users to sign in with Microsoft, you’ll need to register your website with Microsoft first. To do you, you must create an Application Registration in (your tenant’s) Azure Active Directory. Microsoft currently offers two versions of the Azure AD endpoints: v1.0 and v2.0.
To register your WordPress website with Microsoft you should create an Application Registration (see the following online documentation to do so). Once you’ve registered the application you must copy the application’s ID and paste it into this setting.