[MM-29845] Add a new handler to allow authentication via CWS API Key (#16319)

* Add a new handler to allow authentication via CWS API Key

* Make error better

* Add tests and cases for new handler functions

* Move some code around

* Add test for GetCloudSession function

* unset the env after test completion

* Remove white space

* Change Info to Warn

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/session.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"math"
 	"net/http"
+	"os"
 	"time"
 
 	"github.com/mattermost/mattermost-server/v5/audit"
@@ -34,6 +35,21 @@ func (a *App) CreateSession(session *model.Session) (*model.Session, *model.AppE
 	return session, nil
 }
 
+func (a *App) GetCloudSession(token string) (*model.Session, *model.AppError) {
+	apiKey := os.Getenv("MM_CLOUD_API_KEY")
+	if apiKey != "" && apiKey == token {
+		// Need a bare-bones session object for later checks
+		session := &model.Session{
+			Token:   token,
+			IsOAuth: false,
+		}
+
+		session.AddProp(model.SESSION_PROP_TYPE, model.SESSION_TYPE_CLOUD_KEY)
+		return session, nil
+	}
+	return nil, model.NewAppError("GetCloudSession", "api.context.invalid_token.error", map[string]interface{}{"Token": token, "Error": ""}, "The provided token is invalid", http.StatusUnauthorized)
+}
+
 func (a *App) GetSession(token string) (*model.Session, *model.AppError) {
 	metrics := a.Metrics()