Getting issues for getting access token by using trigger and apex class. I am using "https://www.googleapis.com/auth/drive" as callback URL and endpoint of HTTP Request. My create folder method is working properly if valid access token is provided but I am not getting access token. But I am getting error "HTTP method POST is not supported by this URL, StatusCode=405"

Below is my code

```
public class GDriveFolderCreationClass {
private final String clientId ='3MVG98EE59.VIHmz7DO7_********************kb0NbJrDULh.q0CmS3TqSuItCtA6mxyxUaa_STYbpue';
private final String clientSecret = '8E70141F********************6307D13F5B72FD850ABA2C9A05124F3B7B9F';
private final String username = 'test@gmail.com';
public class deserializeResponse{
 public String access_token;
}
public String ReturnAccessToken (GDriveFolderCreationClass acount){
deserializeResponse resp1= new deserializeResponse();
String reqbody = 'client_id='+clientId+'&client_secret='+clientSecret+'&username='+username;
Http h = new Http();
HttpRequest req = new HttpRequest();
req.setBody(reqbody);
req.setMethod('POST');
req.setEndpoint('https://www.googleapis.com/auth/drive');
req.setHeader('Content-Type', 'application/json');
req.setHeader('Accept','application/json');
HttpResponse res = h.send(req);
if(res.getstatusCode() == 200 && res.getbody() != null){
    resp1 = (deserializeResponse)JSON.deserialize(res.getbody(),deserializeResponse.class);
}
return resp1.access_token;
}

@future(Callout=True)
public static void createFolderinDrive(String contentName){ 
GDriveFolderCreationClass account1 = new GDriveFolderCreationClass();
String accessToken;
accessToken = account1.ReturnAccessToken(account1);
createFolder();
}
//Working function for creating folder in google drive
public static void createFolder() {
HttpRequest req = new HttpRequest();
req.setMethod('POST');     
req.setEndpoint('https://www.googleapis.com/drive/v3/files');
req.setHeader('Authorization', 'Bearer '+accessToken);
req.setHeader('content-type', 'application/json');

String body = '{"name" : "'+'TestFolder'+'","mimeType" : "application/vnd.google-apps.folder"}';
req.setTimeout(60*1000);
req.setBody(body);

Http http = new Http();
HttpResponse res = http.send(req);
}
}

```

[ConnectedAppSS](https://i.stack.imgur.com/TA16C.png)
I have also used the AUTH provider and used callback URL as redirect URI but that also didn't worked. For that I am getting below error in debug log
[error ss](https://i.stack.imgur.com/cPW46.png)
Please help me to get access token for my fixed google account to create folder structure in my google drive. Let me know if you want any other details.

Thanks and regards