MSC4079: Server-Defined Client Landing Pages

proposals/4079-client-server-landing-page-html.md

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+# Server-Defined User Home Pages
+
+## Abstract
+This proposal extends the Matrix protocol to allow servers to define custom HTML-formatted documents that can be rendered by clients as a user home page. This feature introduces a non-intrusive yet flexible manner to communicate server-specific information such as donation requests, scheduled maintenance, updates, new features, and changelogs.
+
+## Background
+Currently, there is no standardized method in Matrix for server admins to communicate information directly within user clients. While rooms can serve this purpose, they lack the persistence and prime visibility that many server administrators desire.
+
+## Proposal
+Introduce an optional configuration for matrix servers that allows them to specify an HTML-formatted document, adhering to the current subset of HTML utilized for message formatting. Clients can render this document in a dedicated "home" view or as a placeholder page when no active conversations are selected.
+
+## Use Cases
+
+  - Server administrators want to communicate an upcoming maintenance window without emailing all users.
+  - A non-profit Matrix server could display donation information on the home page to encourage support from its users.
+  - Announcement of new features or user guides following an update can be nicely formatted and made readily available upon client login.
+  - Changelogs for server updates can be displayed, helping users to understand recent changes without external navigation.
+  - Links to other supported clients may be supplied in case users are looking for alternative interfaces.
+
+## Specification
+
+  - A new optional field will be defined within the well-known Matrix configuration for clients: user_home_page.
+  - The user_home_page field can be defined by either in-line HTML content or a fully-qualified domain name and path to an HTML document.
+  - The HTML content will be sanitized by the client and restricted to the subset of HTML currently allowed for messages.
+  - This field can be queried by clients during the login process or refreshed periodically.
+  - Clients may choose to implement this feature as a "home" button or as default content in the main view when no conversation is active.
+
+Example formatting using a file URI:
+
+```
+{
+  "m.user_home_page": {
+    "html_url": "https://your.website/user_home.html"
+  }
+}
+```
+
+Example formatting using in-line HTML:
+
+```
+{
+  "m.user_home_page": {
+    "html_inline": "<h1>Welcome to our Matrix Homeserver!</h1><p>Visit our website to make a donation.</p>"
+  }
+}
+```
+
+## Security Considerations
+To mitigate any potential security risks from malicious content:
+
+  - Clients MUST sanitize the HTML content according to the existing rules for message content sanitation.
+  - External resources (e.g., images, stylesheets) MUST NOT be fetched by default to avoid privacy leaks and must be explicitly allowed by the client.
+
+## Privacy Considerations
+As this feature may potentially be used to track user interaction with the home page content, it's important to:
+
+  - Provide clients the ability to disable external resource fetching.
+  - Ensure that user privacy preferences are respected when displaying this content.
+
+## Conclusion
+This spec change proposal seeks to empower server administrators with the ability to directly communicate important information to their users within the Matrix client, enhancing the user experience by providing relevant and timely information while respecting user privacy and security.