Add RFC: OBS UI Panel APIs

Author: Mitchell Lloyd

text/0000-browser-panel-js-apis.md

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+# Summary
+
+Provide the [JS Bindings API described in the obs-browser
+readme](https://github.com/obsproject/obs-browser#js-bindings) to browser-panels
+(docked UI panels). 
+
+# Motivation
+
+OBS users can embed web UI in OBS that allows them to see information related to
+their broadcast while they are streaming (e.g. Twitch Chat, Stream Statistics).
+However embedded UI does not have access to respond to OBS events or control
+OBS. 
+
+Developers have requested JS APIs for UI panels previously in [GitHub
+comments](https://github.com/obsproject/obs-browser/pull/312#issuecomment-975668271)
+and on ideas.obsproject.com: [Allow use of obs javascript apis in Custom
+Browser
+Docks](https://ideas.obsproject.com/posts/1623/allow-use-of-obs-javascript-apis-in-custom-browser-docks).
+
+I'd like to create an embedded web UI that can add and remove browser sources
+from a scene to streamline the experience of using Twitch's Guest Star features.
+Unifying the JavaScript API bridge between browser sources and UI panels could
+be the first step to enable this and other future use cases.
+
+# Drawbacks
+
+* Opening new APIs to UI panel creates opportunities for security issues where
+  they were previously isolated to browser-sources.
+* This change requires permissions settings for UI panels where there were none 
+  before.
+
+# Additional Information
+
+## Alternatives
+
+**Configure obs-websocket when setting up a service and provide a means to
+exchange the port and password.**
+
+The OBS websocket plugin provides the APIs needed to control OBS from anything
+that can connect to the local websocket. An alternative workflow for creating
+scene sources from a UI panel would require users to copy and paste the port,
+password, and IP address into UI to allow it to control OBS. This requires more
+setup from users and creates an opportunity to break the UI connection (changing
+any of the values or disabling the server).
+
+If the websocket plugin could be configured during service setup (sharing the
+password with the service) and there were some way to detect changes in the
+websocket that would break the connection then this could be a viable
+alternative.
+
+**The [custom URL scheme RFC](https://github.com/obsproject/rfcs/pull/10) could
+allow UI panels to control sources.**
+
+I'm not sure if the current web browser would let OSB users acknowledge that the
+app is open. However this wouldn't provide the two way communication (i.e.
+events are missing) to keep OBS UI in sync with a UI panel.
+
+## Proposal Specifics
+
+In this RFC I'm proposing that we provide JavaScript API parity between
+browser sources
+([obs-browser-source.cpp](https://github.com/obsproject/obs-browser/blob/master/obs-browser-source.cpp))
+and browser panels
+([browser-panel.cpp](https://github.com/obsproject/obs-browser/blob/master/panel/browser-panel.cpp)).
+This requires an introduction of the "Page permissions" concept to UI panels.
+An initial implementation could leave out the UI for managing these permissions,
+only opening permissions when panels are added via services.