[MM-37984] Allow Desktop App to authenticate via external providers outside of the app on supported servers (#24140)

* [MM-37984] Allow Desktop App to authenticate via external providers outside of the app on supported servers

* PR feedback

* Add support for mattermost-dev protocol for development use

* Update server/channels/db/migrations/postgres/000110_create_desktop_tokens.up.sql

* Fix silly typo

* Update server/channels/db/migrations/postgres/000110_create_desktop_tokens.up.sql

* Remove storage of client token, only validate it on the client

* Update migrations

* Add concurrently create index

* Remove CONCURRENTLY for now

* Fix issue with changing history

* Remove old migration

* Use idempotent statement to drop old index

* Remove reference to old table

server/channels/app/oauth.go

@@ -429,7 +429,7 @@ func (a *App) newSessionUpdateToken(app *model.OAuthApp, accessData *model.Acces
 	return accessRsp, nil
 }
 
-func (a *App) GetOAuthLoginEndpoint(w http.ResponseWriter, r *http.Request, service, teamID, action, redirectTo, loginHint string, isMobile bool) (string, *model.AppError) {
+func (a *App) GetOAuthLoginEndpoint(w http.ResponseWriter, r *http.Request, service, teamID, action, redirectTo, loginHint string, isMobile bool, desktopToken string) (string, *model.AppError) {
 	stateProps := map[string]string{}
 	stateProps["action"] = action
 	if teamID != "" {
@@ -440,6 +440,10 @@ func (a *App) GetOAuthLoginEndpoint(w http.ResponseWriter, r *http.Request, serv
 		stateProps["redirect_to"] = redirectTo
 	}
 
+	if desktopToken != "" {
+		stateProps["desktop_token"] = desktopToken
+	}
+
 	stateProps[model.UserAuthServiceIsMobile] = strconv.FormatBool(isMobile)
 
 	authURL, err := a.GetAuthorizationCode(w, r, service, stateProps, loginHint)
@@ -450,13 +454,17 @@ func (a *App) GetOAuthLoginEndpoint(w http.ResponseWriter, r *http.Request, serv
 	return authURL, nil
 }
 
-func (a *App) GetOAuthSignupEndpoint(w http.ResponseWriter, r *http.Request, service, teamID string) (string, *model.AppError) {
+func (a *App) GetOAuthSignupEndpoint(w http.ResponseWriter, r *http.Request, service, teamID string, desktopToken string) (string, *model.AppError) {
 	stateProps := map[string]string{}
 	stateProps["action"] = model.OAuthActionSignup
 	if teamID != "" {
 		stateProps["team_id"] = teamID
 	}
 
+	if desktopToken != "" {
+		stateProps["desktop_token"] = desktopToken
+	}
+
 	authURL, err := a.GetAuthorizationCode(w, r, service, stateProps, "")
 	if err != nil {
 		return "", err