IndieAuth support (#1811)

* Able to authenticate user against IndieAuth. For #1273

* WIP server indieauth endpoint. For https://github.com/owncast/owncast/issues/1272

* Add migration to remove access tokens from user

* Add authenticated bool to user for display purposes

* Add indieauth modal and auth flair to display names. For #1273

* Validate URLs and display errors

* Renames, cleanups

* Handle relative auth endpoint paths. Add error handling for missing redirects.

* Disallow using display names in use by registered users. Closes #1810

* Verify code verifier via code challenge on callback

* Use relative path to authorization_endpoint

* Post-rebase fixes

* Use a timestamp instead of a bool for authenticated

* Propertly handle and display error in modal

* Use auth'ed timestamp to derive authenticated flag to display in chat

* don't redirect unless a URL is present

avoids redirecting to `undefined` if there was an error

* improve error message if owncast server URL isn't set

* fix IndieAuth PKCE implementation

use SHA256 instead of SHA1, generates a longer code verifier (must be 43-128 chars long), fixes URL-safe SHA256 encoding

* return real profile data for IndieAuth response

* check the code verifier in the IndieAuth server

* Linting

* Add new chat settings modal anad split up indieauth ui

* Remove logging error

* Update the IndieAuth modal UI. For #1273

* Add IndieAuth repsonse error checking

* Disable IndieAuth client if server URL is not set.

* Add explicit error messages for specific error types

* Fix bad logic

* Return OAuth-keyed error responses for indieauth server

* Display IndieAuth error in plain text with link to return to main page

* Remove redundant check

* Add additional detail to error

* Hide IndieAuth details behind disclosure details

* Break out migration into two steps because some people have been runing dev in production

* Add auth option to user dropdown

Co-authored-by: Aaron Parecki <aaron@parecki.com>

controllers/controllers.go

@@ -65,3 +65,11 @@ func WriteResponse(w http.ResponseWriter, response interface{}) {
 		InternalErrorHandler(w, err)
 	}
 }
+
+// WriteString will return a basic string and a status code to the client.
+func WriteString(w http.ResponseWriter, text string, status int) error {
+	w.Header().Set("Content-Type", "text/html")
+	w.WriteHeader(status)
+	_, err := w.Write([]byte(text))
+	return err
+}