Question

When designing REST API is it common to authenticate a user first?

The typical use case I am looking for is:

• User wants to get data. Sure cool we like to share! Get a public API key and read away!
• User wants to store/update data… woah wait up! who are you, can you do this?

I would like to build it once and allow say a web-app, an android application or an iPhone application to use it.

A REST API appears to be a logical choice with requirements like this

To illustrate my question I’ll use a simple example.

I have an item in a database, which has a rating attribute (integer 1 to 5).

If I understand REST correctly I would implement a GET request using the language of my choice that returns csv, xml or json like this:

http://example.com/product/getrating/{id}/

Say we pick JSON we return:

{
  "id": "1",
  "name": "widget1",
  "attributes": { "rating": {"type":"int", "value":4} }
}

This is fine for public facing APIs. I get that part.

Where I have tons of question is how do I combine this with a security model? I’m used to web-app security where I have a session state identifying my user at all time so I can control what they can do no matter what they decide to send me. As I understand it this isn’t RESTful so would be a bad solution in this case.

I’ll try to use another example using the same item/rating.

If user “JOE” wants to add a rating to an item

This could be done using:

http://example.com/product/addrating/{id}/{givenRating}/

At this point I want to store the data saying that “JOE” gave product {id} a rating of {givenRating}.

Question: How do I know the request came from “JOE” and not “BOB”.

Furthermore, what if it was for more sensible data like a user’s phone number?

What I’ve got so far is:

1) Use the built-in feature of HTTP to authenticate at every request, either plain HTTP or HTTPS.

This means that every request now take the form of:

https://joe:[e-mail]/product/addrating/{id}/{givenRating}/

2) Use an approach like Amazon’s S3 with private and public key: http://www.thebuzzmedia.com/designing-a-secure-rest-api-without-oauth-authentication/

3) Use a cookie anyway and break the stateless part of REST.

The second approach appears better to me, but I am left wondering do I really have to re-invent this whole thing? Hashing, storing, generating the keys, etc all by myself?

This sounds a lot like using session in a typical web application and rewriting the entire stack yourself, which usually to me mean “You’re doing it wrong” especially when dealing with security.

EDIT: I guess I should have mentioned OAuth as well.

Answer 1

Edit 5 years later

Use OAuth2!

Previous version

No, there is absolutely no need to use a cookie. It’s not half as secure as HTTP Digest, OAuth or Amazon’s AWS (which is not hard to copy).

The way you should look at a cookie is that it’s an authentication token as much as Basic/Digest/OAuth/whichever would be, but less appropriate.

However, I don’t feel using a cookie goes against RESTful principles per se, as long as the contents of the session cookie does not influence the contents of the resource you’re returning from the server.

Cookies are evil, stop using them.