Background
I have a RESTful API accessed through the domain http://restapi.com
I have a client app using http://restapi.com
. The client app has the domain http://myapp.com
The way I have my HATEOAS setup is that the API presents URIs without a domain. So instead of http://restapi.com/some/resource
, it contains links to resources like so /some/resource
. Example API json resource below:
{"_links":{"self":{"href":"/some/resource"}}}
The benefit this has is that the API doesn't need to know about the client app, and the client app has to do very little to get the correct resource from the API and doesn't have to reformat all the URIs in the resource. For example, in the client app, the following URI would be used by the browser http://myapp.com/some/resource
. When the app gets the request, it then needs to call the API to get the resource and simply swaps the domain i.e. http://restapi.com/some/resource
.
This has been successful so for, and allows a lot of flexibility to have different clients use the API with the only knowledge required being the initial end point (domain) of the API. It also completely decouples the API from the client apps.
The problem I have run into is that I have started using some external services (specifically PayPal adaptive payments) where I need to provide a redirect URL for cancelled payments and successful payments. For example, the browser navigates to http://myapp.com/payment
. The resource returned by http://restapi.com/payment
presents a link to PayPal. Without going into too much detail, the API has to ask PayPal for a payment ID, which can then be used to create a link to a PayPal payment e.g. http://paypal.com?PayId-123456
. Part of the creation process requires that URLs are provided to redirect on payment cancellation or success. Again, don't want to go into details, but when requesting a PayId from PayPal, the redirect URLs are sent as variables to PayPal, and I guess PayPal stores them against the specific PayId created.
The browser navigates to the link returned in the resource - http://paypal.com?PayId-12345
. Payment is made and PayPal then uses the redirect URLs as needed to redirect back to my app e.g. on successful completion of payment, PayPal should redirect to http://myapp.com/paymentcomplete
. Note: I realise that this is not a restfully named URI, but it simplifies building up the description of my problem
Problem
The problem I have may now be obvious. I need to redirect back to http://myapp.com/paymentcomplete
, BUT its the API that provides the redirect URL to PayPal. It has no knowledge of the client application. Since PayPal is an external service, the full URL must be provided. The best the API can do is send http://restapi.com/paymentcomplete
as the redirect URL, but if PayPal redirects to this, the resulting response will be a JSON string (the output format of my API) not the nicely formatted page of the client app.
My question is, what is a good way to correctly provide the redirect URL to PayPal?
One thought I had was to make the client application handle creating the PayPal PayId, but I don't like this option as I would like to keep the creation of the PayPal payment ID on the API side. It would also require every client app to provide its own implementation, something I also don't want.
The other option I though of was to ask the client to provide its domain in the request. Currently the request the client makes to get the resource with the link to PayPal is GET http://restapi.com/payment
, but I could use POST http://restapi.com/payment
with the client providing its domain as a param. The API can then use this to construct the correct redirect URL. I don't really like this idea either as its seems a bit hackish and also requires the app to know that is must fill in this field i.e. a human user wouldn't fill the domain input in.
Additional solutions, or thoughts greatly welcomed.