How do I authenticate users to sites in different domains?

I have a Node.js API on api.com that authenticates users based on Sessions. How can I save session from api in api.com to client.com?

For example; I'm going to send a request from client.com to api.com and add a session cookie to client.com from the api on api.com.

My session settings;

app.use(session({
    secret: process.env.SECRET,
    resave: false,
    saveUninitialized: false,
    store
}))