[rizlas]

As discussed #1378 this adds per provider settings to customize the login button.

Setting	Description
appearance-icon	Login button icon, as a base64 image data URI
appearance-button-background-color	Login button background color, as a hex color

Both values are validated before being added to the login page. The CSS is injected by a listener on BeforeLoginTemplateRenderedEvent, and each provider button gets the oidc-provider-<id> class, so it works on both NC < 34 (OC_App::registerLogIn) and NC >= 34 (IAlternativeLoginProvider).

🤖 AI (if applicable)

• AI was used to help me adapt this feature to the current alternative login code and to test it on fully functional Nextcloud instances (33 and 34).

[github-actions]

Hello there,
Thank you so much for taking the time and effort to create a pull request to our Nextcloud project.

We hope that the review process is going smooth and is helpful for you. We want to ensure your pull request is reviewed to your satisfaction. If you have a moment, our community management team would very much appreciate your feedback on your experience with this PR review process.

Your feedback is valuable to us as we continuously strive to improve our community developer experience. Please take a moment to complete our short survey by clicking on the following link: https://cloud.nextcloud.com/apps/forms/s/i9Ago4EQRZ7TWxjfmeEpPkf6

Thank you for contributing to Nextcloud and we hope to hear from you soon!

(If you believe you should not receive this message, you can add yourself to the blocklist.)