{"error":"unsupported_grant_type","error_description":"grant type not supported"}

public class SalesforceAuthentication
{
    public SalesforceAuthentication()
    {
    }
    public static void authenticate()
    {
        string authUrl = 'https://login.salesforce.com/services/oauth2/token';
        HttpRequest req = new HttpRequest();
        req.setEndpoint(authUrl);
        req.setMethod('POST');
        req.setBody('grant_type=password&client_id=3MVG9ZL0ppGP5UrBcvLyXYRmRUuYKSgFgQayclpZBWmbi7PQ2vWj1V8Xev.GfE0C9xyWMrTzONlj2GZ0ow6VK&client_secret=2150505966475551576&username=manoj6893@gmail.com&password=manoj438sKQzXe5pXoMwIDn1IOIFZqQt');
        Http http = new Http();
        HttpResponse response = http.send(req);

        AuthWrapper aw = (AuthWrapper)JSON.deserialize(response.getBody(),AuthWrapper.class);
        system.debug('auth response..!'+aw);

        String serviceUrl = aw.instance_url+'/services/apexrest/Account/0012800000ro2xS';
        req = new HttpRequest();
        req.setEndpoint(authUrl);
        req.setMethod('GET');
        req.setHeader('Authorization','Bearer '+aw.access_token);
        req.setHeader('Content-Type','application/json');
        response = http.send(req);
        system.debug('server response..!'+response.getBody());
    }

    public class AuthWrapper
    {
        public string access_token;
        public string instance_url;
        public string id;
        public string issued_at;
        public string signature;
    }
}