public static void test(){

    String clientId = '3MVG9U_dUptXGpYIT.RB2JJXp.LMAoiYwISAmLt_9VcpgVnqVyUxS8qBvLAUugR1olAf3ysw5vDsO2fcr.TsQ';
    String clientsecret = '4163901141616295076';
    String username = 'stifel-rst@silverlinecrm.com.rstdev';
    String SecurityToken = 'dWB5m6BSUicCFGuQw5n1c0kB';
    String password = 's*******'+SecurityToken;
    String reqbody = 'grant_type=password&client_id='+clientId+'&client_secret='+clientsecret+'&username='+username+'&password='+password;
    Http h= new Http();

    HttpRequest req= new HttpRequest();
    req.setBody(reqbody);
    req.setMethod('POST');
    req.setEndpoint('https://test.salesforce.com/services/oauth2/token');
    System.debug('request'+req.getBody());
    HttpResponse res=h.send(req);
    System.debug('res::'+res);
}