Bug in calculation of oauth_body_hash parameter. Fix is trivial

[dvishniakov]

Summary

oauth_body_hash parameter is incorrectly calculated

Simplest Example to Reproduce

request({
    method: "POST",
    headers: [
      {
        name: "content-type",
        value: "application/xml"
      }
    ],
    url: "any_valid_url",
    body: "Hello World!",
    oauth: {
      body_hash: true,
      consumer_key: "jisc.ac.uk",
      consumer_secret: "secret",
      transport_method: "header",
    }
  }),

Expected Behavior

oauth_body_hash should be equal to "Lve95gjOVATpfV8EL5X4nxwjKHE"
Have a look at example here: https://tools.ietf.org/id/draft-eaton-oauth-bodyhash-00.html#anchor15
Or using an online tool: https://www.online-convert.com/result/df6e64e9-bc92-4ff3-b849-0c8f003c7e3c

Current Behavior

oauth_body_hash is calculated incorrectly. When using request-debug:

REQUEST make request http://ltiapps.net/test/tc-outcomes.php
{ request: 
   { ...,
     headers: 
      { ...,
        'content-length': 12,
        Authorization: 'OAuth oauth_body_hash="MmVmN2JkZTYwOGNlNTQwNGU5N2Q1ZjA0MmY5NWY4OWYxYzIzMjg3MQ%3D%3D",oauth_signature_method="HMAC-SHA1",..."' },
     body: 'Hello World!' } }

Possible Solution

PR is linked

Context

This issue fails my requests to IMS LTI Outcome service which requires POST requests and body hashes.

@simov FYI

[dvishniakov]

@mikeal any ideas how is it possible to make some progress here? Thanks