GraphController.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Graph;
using Microsoft.Identity.Client;

[Authorize]
[ApiController]
[Route("api/[controller]")]
public class GraphController : ControllerBase
{
    private GraphClient graphClient;

    public GraphController(GraphClient client)
    {
        graphClient = client;
    }

    [HttpGet]
    public async Task<IEnumerable<object>> Get()
    {
        IEnumerable<User> users;

        try
        {
            users = await graphClient.ServiceClient.Users.Request().GetAsync();
        }
        catch (MsalUiRequiredException ex)
        {
              graphClient.AuthenticationProvider.Token.ReplyForbiddenWithWwwAuthenticateHeader(graphClient.AuthenticationProvider.Scopes, ex);
            throw ex;
        }
        catch (Exception)
        {
            throw;
        }

        return users.Select(x => new
        {
            name = x.DisplayName,
            upn = x.UserPrincipalName,
            mail = x.Mail,
            city = x.City,
            jobTitle = x.JobTitle,
            image=x.Photo
        });
    }

    [HttpGet("{upn}")]
    public async Task<object> Get(string upn = "me")
    {
        User user;
        try
        {
            if (upn.Equals("me"))
            {
                user = await graphClient.ServiceClient.Me.Request().GetAsync();
            }
            else
            {
                user = await graphClient.ServiceClient.Users[upn].Request().GetAsync();
            }
        }
        catch (MsalUiRequiredException ex)
        {
            graphClient.AuthenticationProvider.Token.ReplyForbiddenWithWwwAuthenticateHeader(graphClient.AuthenticationProvider.Scopes, ex);
            throw ex;
        }
        catch (Exception)
        {
            throw;
        }

        return new
        {
            name = user.DisplayName,
            upn = user.UserPrincipalName,
            mail = user.Mail,
            city = user.City,
            jobTitle = user.JobTitle,
            image = user.Photo
        };
    }
}