Add support for PLAINTEXT signature method

[simov]

I was trying to authenticate to Freshbooks using request, and it turned out that they currently support only PLAINTEXT as a signature method http://developers.freshbooks.com/authentication-2/

So I read about it here http://oauth.net/core/1.0/#anchor22 and I figured that it should be the same as the hmacsign minus the base string.

Now obviously the first 3 arguments are not needed in this case, but I kept them here because I just pointed my request's oauth-sign dependency to my patched version and it worked

I can remove these 3 arguments and after this is being published I can patch the request's source code as well, or we can just leave it as it is. Let me know what do you think.

Also summoning @nylen

[nylen]

I don't like the extra arguments because we export plaintext as its own function. We should not change the signature of sign though, so you could do something like this:

var method
var skipArgs = 1
...
  case 'PLAINTEXT':
    method = plaintext
    skipArgs = 4
...
return method.apply(null, [].slice.call(arguments, skipArgs))

[simov]

Right, @nylen can you take a look at my last commit as well? I just added 2 simple unit tests to prove our point.

[nylen]

👍

New npm version coming up shortly, then I can write tests and docs this week and get this merged into request, unless you want to beat me to it :)

[nylen]

version 0.6.0 is out.

[simov]

Thanks, about request - that would be great, let me know if I need to add anything about this feature there 👍