I’m happy to report that we’ve fixed an issue in the percent encoding step of our OAuth signature library for the Jersey framework. The issue reported was caused by the fact that we were using Java’s URLEncoder and URLDecoder classes to compute OAuth’s signature base string. Unfortunately those classes do not perform an RFC3986 compliant encoding which is required in OAuth. The main difference is that a space character will be encoded as a + when we need it to be escaped as a %20 (more info here).

To fix this, we’ve chosen to leverage Jersey’s UriComponent class. There is one notable difference though with how one would encode a URI (see here for a very detailed explanation of URIs): OAuth says that the signature base string is built by concatenating the request method, the request URL and the normalized parameters (with & to separate them) and that those elements must be encoded (prior to concatenation). In effect we are re-encoding elements that are already encoded. As Paul noted, it’s as if we wanted to pass the signature base string in a URI… I remember this possibility was mentioned in conversations about debugging OAuth deployment but that’s the only case I remember for this.

Anyway, to illustrate this, below is the piece of code where the bulk of the action happens:

StringBuffer buf = new StringBuffer(request.getRequestMethod().toUpperCase());
URI uri = constructRequestURL(request);
String tp = uri.getScheme();
buf.append('&').append(UriComponent.encode(tp, UriComponent.Type.SCHEME));
tp = uri.getAuthority();
buf.append("%3A%2F%2F").append(UriComponent.encode(tp, UriComponent.Type.AUTHORITY));
tp = uri.getPath();
buf.append(UriComponent.encode(tp, UriComponent.Type.PATH_SEGMENT));
buf.append('&').append(UriComponent.encode(normalizeParameters(request, params), UriComponent.Type.QUERY_PARAM));

Our testing code now also includes elements with spaces to make sure we got it right (thanks to Michael Werle).