Provides functions for generating requests, and parsing responses necessary
for integrating with three-legged OAuth 1.0 providers like Twitter.

All Token requests and Protected Resources requests MUST be signed by the
Consumer and verified by the Service Provider. The purpose of signing requests
is to prevent unauthorized parties from using the Consumer Key and Tokens when
making Token requests or Protected Resources requests. The signature process
encodes the Consumer Secret and Token Secret into a verifiable value which is
included with the request.

OAuth does not mandate a particular signature method, as each implementation
can have its own unique requirements. The protocol defines three signature
methods: HMAC-SHA1, RSA-SHA1, and PLAINTEXT, but Service Providers are free to
implement and document their own methods. Recommending any particular method
is beyond the scope of this specification.

The Consumer declares a signature method in the `oauth_signature_method`
parameter, generates a signature, and stores it in the `oauth_signature`
parameter. The Service Provider verifies the signature as specified in each
method. When verifying a Consumer signature, the Service Provider SHOULD check
the request nonce to ensure it has not been used in a previous Consumer
request.

The signature process MUST NOT change the request parameter names or values,
with the exception of the `oauth_signature` parameter.

For more information refer to the OAuth 1.0 specification at
http://oauth.net/core/1.0/#signing_process.