Programming Social Applications

Tools and Tips for Debugging Signature Issues

In this section, we’ll dive into the most common OAuth issues and go over tips and tricks to address them.

Missing or duplicate parameters

One of the single most frustrating experiences you’ll run into when working with OAuth is to see a “signature mismatch” or “signature invalid” response sent back from a request. If you haven’t encountered this error very often, you might end up spending hours trying to debug signatures to figure out where the problem lies.

In most cases, invalid signature errors are produced for two reasons:

• You have forgotten a parameter in the request.

• You have duplicated a parameter in the request.

In the case of forgotten parameters, there are two techniques that work well to help you debug the signature issues. The first, and easiest, is to compare the invalid signature parameters against those expected at the OAuth stage where the error was produced. You can compare these parameters against those listed earlier in this chapter in the section OAuth 1.0a Workflow. You should be able to determine fairly quickly whether a missing parameter is the cause.

The other method involves comparing exact signatures. If you have access to valid signatures from the same platform (either through docs or another application), you can compare them to your invalid signatures to pinpoint discrepancies. This method comes in handy if you are aiding a development team that’s encountering issues when you have an existing, functional application. ...