Revert "[MM-51274] Remove deprecated PermissionUseSlashCommands (#22819)" (#23405)

Automatic Merge

server/channels/api4/command.go

@@ -329,6 +329,13 @@ func executeCommand(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// For compatibility reasons, PermissionCreatePost is also checked.
+	// TODO: Remove in 8.0: https://mattermost.atlassian.net/browse/MM-51274
+	if !c.App.SessionHasPermissionToChannel(c.AppContext, *c.AppContext.Session(), commandArgs.ChannelId, model.PermissionUseSlashCommands) {
+		c.SetPermissionError(model.PermissionUseSlashCommands)
+		return
+	}
+
 	channel, err := c.App.GetChannel(c.AppContext, commandArgs.ChannelId)
 	if err != nil {
 		c.Err = err
@@ -347,6 +354,13 @@ func executeCommand(c *Context, w http.ResponseWriter, r *http.Request) {
 				c.SetPermissionError(model.PermissionCreatePost)
 				return
 			}
+
+			// For compatibility reasons, PermissionCreatePost is also checked.
+			// TODO: Remove in 8.0: https://mattermost.atlassian.net/browse/MM-51274
+			if !c.App.SessionHasPermissionTo(*c.AppContext.Session(), model.PermissionUseSlashCommands) {
+				c.SetPermissionError(model.PermissionUseSlashCommands)
+				return
+			}
 		}
 	}