Setting up Gmail SMTP on behalf of a client

Is it possible to setup the Gmail SMTP authentication using general developer API credentials? We manage a bunch of different websites and it would be great to have the ability to create the Client ID and Secret key as needed, without requiring the actual Gmail password of the client.

This concerns me because a few of my clients have sensitive information in their email and they don’t feel comfortable giving up a password. On top of this, if they do give me their password for this process and then change it some time in the future, the authentication stops working.

Does anyone have a workaround for this situation?