[MM-37984] Allow Desktop App to authenticate via external providers outside of the app on supported servers (#23795)

* WIP

* Add rate limiting for desktop token API

* Missing mocks

* Style fixes

* Update snapshots

* Maybe use an actual redirect link :P

* Refactoring for tests

* Add tests for server

* Fix lint issue

* Fix tests

* Fix lint

* Add front-end screen component

* Component logic

* Style changes

* Quick style fix

* Lint fixes

* Initial PR feedback

* Enable logging into the browser as well when completing the login process

* Refactor to push more logic to the other component

* Remove unnecessary helper code

* Fix i18n

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/oauth.go

@@ -431,7 +431,7 @@ 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 != "" {
@@ -442,6 +442,10 @@ 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)
@@ -452,13 +456,17 @@ 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