Extracting OAuth 2.0 token in response to request by ServiceCallout

[HamzaJaffry]

hi guys I am new to this, I have been searching for a long time to find a method for my proxy to send a request to another that uses Auth 2.0 for verification, I am doing it by a service callout , however I am successfully receiving the token in the response but am not able to extract the token from it using extract variable but the variable remains empty, if i define the source in the EV it says that the message is not available to the EV policy . Then saw it in one of the documentation that the extract variable works only on "application/json" and not "application/x-www-form-urlencoded" so i attached a javascript policy to do so but still unsuccessful in retrieving the token from the response, i would appreciate some guidance on it.

SC policy

<ServiceCallout name="SC-GetOAuthToken">
  <DisplayName>SC-GetOAuthToken</DisplayName>
  <Request variable="oauthRequest">
    <Set>
      <Verb>POST</Verb>
      <Headers>
        <Header name="Content-Type">application/x-www-form-urlencoded</Header>
      </Headers>
      <FormParams>
        <FormParam name="client_id">{CLIENT_ID}</FormParam>
        <FormParam name="client_secret">{CLIENT_SECRET}</FormParam>
        <FormParam name="grant_type">client_credentials</FormParam>
        <FormParam name="scope">{SCOPE}</FormParam>
      </FormParams>
    </Set>
  </Request>
  <Response variable="NewTokenVariable"/>
  <HTTPTargetConnection>
    <URL>{SERVICE_URL}</URL>
  </HTTPTargetConnection>
</ServiceCallout>

ev policy: 

<ExtractVariables name="EV-ExtractOAuthToken">
  <DisplayName>Extract OAuth Token</DisplayName>
  <JSONPayload>
    <Variable name="access_token" type="string">
      <JSONPath>$.access_token</JSONPath>
    </Variable>
    <Variable name="token_type" type="string">
      <JSONPath>$.token_type</JSONPath>
    </Variable>
    <Variable name="expires_in" type="integer">
      <JSONPath>$.expires_in</JSONPath>
    </Variable>
    <Variable name="consented_on" type="integer">
      <JSONPath>$.consented_on</JSONPath>
    </Variable>
    <Variable name="scope" type="string">
      <JSONPath>$.scope</JSONPath>
    </Variable>
  </JSONPayload>
  <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
  <Source>NewTokenVariable</Source>
</ExtractVariables>

JS step:

var tokenResponse = context.getVariable("NewTokenVariable");
print("Token Response: " + tokenResponse);
if (tokenResponse) {
  var jsonResponse = JSON.parse(tokenResponse);
  var accessToken = jsonResponse.access_token;
  context.setVariable("extractedAccessToken", accessToken);
  print("Access Token Extracted: " + accessToken);
} else {
  print("NewTokenVariable is null or empty");
  context.setVariable("extractedAccessToken", "Token Not Found");
}

just for reference this is the type of response generated by my SC,  is something like this

{
"token_type": "Bearer",
"access_token": "{ACCESS_TOKEN}",
"expires_in": {EXPIRES_IN},
"consented_on": {CONSENTED_ON},
"scope": "{SCOPE}"
}