URL Preview for private URLs with active integrations (GitHub, GitLab, Jira)

[almereyda]

Your use case

Posting this here, as this is where the proposal will become visible to a person that is using Element.

What would you like to do?

When pasting a link to an issue in a private GitLab repository, I would like to see an informative URL preview.

This might also be valid for the prime integrations with GitHub and Jira.

Why would you like to do it?

When referencing people to items in private repositories, in rooms with link previews enabled, we are regularly presented with the login screen. Clicking it away is a little tedious and could potentially be avoided.

How would you like to achieve it?

Paste a URL into a private GitLab repository / group / instance.

URL preview knows how to fetch the sensitive metadata.

This could maybe be facilitated by an existing Hookshot integration. Possibly by providing an oEmbed endpoint with a hardly guessable URL that does the resolution against GitLab?

This appears to become more challenging, if multiple integrations to multiple GitLab (GitHub (Enterprise), Jira) instances are considered.

Have you considered any alternatives?

1. Disabling URL previews for the whole room is a poor workaround.
2. Using url_preview_url_blacklist in Synapse and adding rules for private instances / groups / repositories there.
3. Allow Element to build the preview locally via CORS and post it to the channel. Archive URL preview content at the time it is posted to a room #10676

Additional context

References

• URL Preview GitHub/GitLab file URLs with code snippets element-meta#1295
• Gitter feature parity overview issue roadmap#26
• [WIP] MSC2370: Resolve URL API matrix-org/matrix-spec-proposals#2370

• matrix-org/matrix-hookshot
• Setting up GitLab, Git... | Element Knowledge

• Use oembed for url previews? matrix-org/synapse#2752
  • Allow configuration of the oEmbed URLs. matrix-org/synapse#10714
    • e2481db
• Link preview should respect robots.txt #3242
• Skip URL previews of login pages #3440
• URL preview whitelisting akin to url_preview_url_blacklist #6205
• Repair URL preview for tweets, may require a logged in Twitter account matrix-org/synapse#7643
  • Support oEmbed for media previews. matrix-org/synapse#7920
    • 3fc8fdd
• Dynamically fetch oembed provider metadata (for url previews) #9877
• Archive URL preview content at the time it is posted to a room #10676
• Handle structured data (JSON-LD / Microdata / RDFa) for URL previews #11540
• Ability to configure User-Agent for URL previews #17873
  • feat: support for setting UA for URL previews #17968

[Half-Shot]

When referencing people to items in private repositories, in rooms with link previews enabled, we are regularly presented with the login screen. Clicking it away is a little tedious and could potentially be avoided.

IIRC, It's not helped that GitLab's response to unauthenticated access is to redirect you to the login screen so it's hard for Synapse to figure out that it's not a valid preview.