Cloud functions reverse proxy for multiple domains

[Laurent Pellegrino]

Hello,

I am using Firebase for a service used by multiple customers. 

My service allows customers to create a project and then to list public information for this project at an URL that includes the project ID as HTTP parameter.

Firebase hosting is configured to use a custom domain: mydomain.com.

The response is created by a Firebase HTTP function based on the project ID.

 

Hosting requests to /project redirect to a Cloud Function using a rewrite.

At the end, a customer uses https://mydomain.com/project?id=xyz to access the public page.

My next step is to offer the possibility for customers to use their own domain for the public page. For instance, if a customer uses https://customer.com/project, then the resulting page is the same as https://mydomain.com/project?id=xyz.

The project ID is deduced from the customer domain or subdomain used.

I wonder if the current Firebase features and Cloud functions allow such kind of reverse proxy use case. I really like the possibility to control CDN caching from Cloud functions.

Before asking on this group I made a few tests. Currently, I am facing 2 issues for achieving what I would like to do:

1) How to retrieve the original request domain from a Cloud function?

I tried the following:

exports.test = functions.https.onRequest((req, res) => {
    const host = req.get('host');
    const origin = req.get('origin');


    console.log('host=' + host);
    console.log('origin=' + origin);


    res.send(200, {
        'host': host,
        'origin': origin,
    });
});

Unfortunately, when I call https://mydomain.com/test, I get undefined for origin and us-central1-XXX.cloudfunctions.net for host where XXX is my project name.

2) Firebase hosting allows connecting multiple domains. However, is there a limit on the number of domains? More importantly, is there an API to automate the creation of such connections?

Any ideas and suggestions are welcome.

Kind Regards,

Laurent Pellegrino