Access denied by Business Data Connectivity

While creating an external content type in SharePoint Designer 2013 the following error was displayed when adding a connection to an SQL server using an impersonated custom identity:

Access denied by Business Data Connectivity

This occurred because the user does not have Edit permission on the BDC metadata catalog.  To grant access requires only a few steps:

1. In Central Administration, under Application Management, click Manage Service Applications
2. Click the Business Data Connectivity service
3. Click Set Metadata Store Permissions
4. Add the required user and grant Edit permissions.  Click OK
   

Now the connection can be created successfully in SharePoint Designer.