Better UX in GUI apps

[lidel]

Continued from #6, see also #7

Now that #14 is merged, and we got the basic minimum (support for Authorization: Bearer <key>) we could discuss ways to improve UX of adding services, namely avoid manual copying of authorization token from pinning service to GUI app interface.

To illustrate UX needs, adding pinning service to WebUI in IPFS Desktop app could look like this:

1. User goes to Settings screen and clicks on "Add Pinning Service"
2. List of predefined services is shown (there is also "Custom" option for manual config)
3. User clicks on one of predefined providers
4. WebUI opens authorization page at Pinning Service (PS) using well known API endpoint (passing any data that is required)
5. PS provides interface for "granting pinning permissions to the app X" (page could also enable user to create a new pin space, or attach WebUI to existing one)
6. Upon user approval via PS interface, WebUI is able to use configured pinning service (without copying anything manually)

Qs:

• Any prior art comes to mind? We'd rather not reinvent wheel, if possible
• Do we need to return anything back to WebUI in step 6, if we generate sufficiently random token on the client and pass it in step 4? (randomness could be augmented by drand)

[jessicaschilling]

This is pretty standard flow. One thing to note: if we go down this route, it would be good to provide guidance (not requirements, just guidance) for how pinning services may wish to present their own auth page for consistency.

My only concern here is that it would create a higher barrier to entry to creating a pinning service that integrates with Desktop/Web UI -- the creator of the service actually has to build this auth flow on their end. If I was running a micro-pinning service for small-scale needs, I might not want to bother with this.