REST API to attachment thumbnails

[Krzysztof Surdacki]

We are migrating our app from Connect to Forge and we are looking the way to download attachment thumbnail using system/user token provided by Forge. Similar to 

`GET /wiki/rest/api/content/{id}/child/attachment/{attachmentId}/download`, but for a thumbnail or `GET /rest/api/3/attachment/thumbnail/{id}` Jira equivalent.

[James Thompson]

You can try using the Forge REST API endpoint for attachments with query parameters to request a thumbnail. Typically, Forge doesn’t provide a dedicated “thumbnail” endpoint like Jira Cloud REST, but you can use the GET /wiki/rest/api/content/{id}/child/attachment/{attachmentId} endpoint and inspect the metadata or mediaType fields. Many attachments include a representation object with a thumbnail URL you can fetch directly using the same Forge auth token.

Make sure your app has the read:confluence-content or read:confluence-user scopes depending on whether it’s a system or user token.

If the attachment doesn’t include a thumbnail automatically, you may need to generate it server-side after downloading the full attachment.

[Krzysztof Surdacki]

There is no `read:confluence-content` scope permission, maybe `read:confluence-content.all`? My test permissions scopes are:

read:app-user-token: {}
read:app-system-token: {}
read:content:confluence: {}
read:content-details:confluence: {}
read:page:confluence: {}
read:blogpost:confluence: {}
read:attachment:confluence: {}
read:confluence-content.summary: {}
read:confluence-content.all: {}
readonly:content.attachment:confluence: {}
read:hierarchical-content:confluence: {}
read:space:confluence: {}

`GET /wiki/rest/api/content/{id}/child/attachment/{attachmentId} ` returns `405 Method Not Allowed` when invoked from a web browser and `401 Unauthorized; scope does not match` when called with Forge system token either from `GET https://api.atlassian.com/ex/confluence/{cloudId}/rest/api/content/{contentId}/child/attachment/{attachmentId}` or `GET https://api.atlassian.com/ex/confluence/{cloudId}/wiki/rest/api/content/{contentId}/child/attachment/{attachmentId}`