Support avatars being external URL or being base64-encoded

[richardhj]

From what it looks like, the user blueprint MUST have field "avatar" and this field MUST be of type asset. This approach does not work when working with external authentication providers.

https://github.com/statamic/cms/blob/85265e6e987ec2c5f1566fdd01b22f2d7a3ad89d/src/Auth/HasAvatar.php#L17

I am using the Socialite provider "microsoft" and this provider returns the avatar base64-encoded. This value is just ignored by Statamic, even using data:image/png;base64, XXX as a value does not work. The provider could also return a full URI.

How to reproduce

# /users/[email protected]
name: 'Foo'
avatar: '/9j/4AAQSkZJRgABAQEAYABgAAD/2wBDAA'

AppServiceProvider.php

// AppServiceProvider.php

Event::listen(function (SocialiteWasCalled $event) {
      $event->extendSocialite('microsoft', MicrosoftProvider::class);
  });

OAuth::provider('microsoft')
    ->withUserData(fn (SocialiteUser $socialiteUser, StatamicUser $statamicUser) => [
        'name' => $socialiteUser->getName(),
        'avatar' => $socialiteUser['avatar'],
    ]);

// services.php

return [
    'microsoft' => [
        // ...
        'include_avatar' => true,
    ],
];