title: Gatling Generate OAuth2.0 token using callback URL not working
body: <p>Here is my scenario.</p>
  
  <pre><code>val header = Map(
      "Accept" -&gt; """application/json""",
      "Content-Type" -&gt; """application/x-www-form-urlencoded, charset=UTF-8""")
  
  val auth_token = scenario("POST Authentication")
          .exec(
              http("POST OAuth Req")
              .post("/validate/activationURL")
              .formParam("oauth.token.client.secret", "*******")
              .formParam("oauth.token.url", "https://myweb.com/as/token.oauth2")
              .formParam("oauth.token.client.id", "my-test-user")
              .formParam("oauth.token.grant.type", "client_credentials")
              .formParam("oauth.token.scope", "my:test:activation")
              .headers(header)
      )
  </code></pre>
  
  <p>But I'm getting error as</p>
  
  <pre><code>=========================
  HTTP request:
  POST https://my-validation.net/validate/activationURL
  headers=
  Accept: application/json
  Content-Type: application/x-www-form-urlencoded
  Content-Length: 305
  Host: https://my-validation.net/
  params=
  oauth.token.client.secret: *******
  oauth.token.url: https://myweb.com/as/token.oauth2
  oauth.token.client.id: my-test-user
  oauth.token.grant.type: client_credentials
  oauth.token.scope: my:test:activation
  =========================
  HTTP response:
  status=
  401 Unauthorized
  headers= 
  Cache-Control: no-store
  Content-Type: application/json;charset=UTF-8
  Date: Fri, 03 Feb 2017 03:30:40 GMT
  Pragma: no-cache
  Strict-Transport-Security: max-age=31536000 ; includeSubDomains
  Www-Authenticate: Bearer realm="oauth2-resource", error="unauthorized", error_description="Full authentication is required to access this resource"
  X-Cf-Requestid: 4681a3da-a747-40f7-4801-b6b972b07cf6
  X-Content-Type-Options: nosniff
  X-Frame-Options: DENY
  X-Xss-Protection: 1; mode=block
  Content-Length: 102
  
  body=
  {"error":"unauthorized","error_description":"Full authentication is required to access this resource"}
  &lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;
  20:30:40.972 [DEBUG] i.g.h.a.ResponseProcessor - 
  &gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;
  </code></pre>