[SalesForce] unable to generate access token for OAUTH 2.0

I am trying to generate the access token using OAUTH 2.0 . Here is the full code but repsonse.getBody() is not giving me the JSON string.

I have 2 instances of salesforce sandbox api, data flow is from salesforceA(source) to salesforceB(destination)

Both users are having system admin profile.

In salesforceA(source) I have created a connected app, so I get clientID and client secret, callback URL is: http://ap2.salesforce.com/apex/MyResponse
where Myresponse is a visualforce page.

In salesforceB(destination), in remote site settings I have registered the URL
"https://login.salesforce.com/services/oauth/token'

apex controller and visual force page is in salesforceB(destination)

public class restExample1
{
  public String ClientSecret{get;set;}
  public String ClientID{get;set;}
  public String UserName{get;set;}
  public String Password{get;set;}
  public String Result{get;set;}
  public String accessToken{get;set;}


  public PageReference GetAccessToken()
  {
HttpRequest request=new HttpRequest();

request.setEndPoint('https://login.salesforce.com/services/oauth/token');

request.setMethod('POST');

String reqbody = 'grant_type=password&client_id='+clientId+'&client_secret='+clientSecret+'&username='+username+'&password='+password;

request.setBody(reqbody);

Http p=new Http();

HttpResponse response=p.send(request);

result=response.getBody();

system.debug('@@@result = '+result);

return null;
}
}

Myresponse visualforce page

<apex:page controller="restExample1">
<apex:form >
  <apex:pageBlock title="RestApiExample">

       <apex:pageBlockSection title="OAuth2.0 username & Password"
                              collapsible="false">


       <apex:pageBlockSectionItem >
            <apex:outputLabel value="ClientID"/>

            <apex:inputText value="{!ClientID}"/>

       </apex:pageBlockSectionItem>

       <apex:pageBlockSectionItem >
            <apex:outputLabel value="ClientSecret"/>

            <apex:inputText value="{!ClientSecret}"/>

       </apex:pageBlockSectionItem>


       <apex:pageBlockSectionItem >
            <apex:outputLabel value="UserName"/>

            <apex:inputText value="{!UserName}"/>

       </apex:pageBlockSectionItem>

       <apex:pageBlockSectionItem >
            <apex:outputLabel value="Password"/>

            <apex:inputText value="{!Password}"/>

       </apex:pageBlockSectionItem>


       </apex:pageBlockSection>

       <apex:pageBlockButtons >

         <apex:commandButton value="Get Access Token"
                             action="{!GetAccessToken}"
                             reRender="token"/>

       </apex:pageBlockButtons>
  </apex:pageBlock>

  <apex:pageBlock title="Access Token"
                  id="token">


     {!accesstoken}

   </apex:pageBlock>

</apex:form>

</apex:page>