Generate access token with IdentityServer3 without password

Question

How to manually generate access_token from server without password? I want to allow super admins login as users and look at their problems and see the problems by their eyes, so i need user access_token. i already see this question but didn't help me in IdentityServer3.

Answer 1

first create a custom grant named loginBy

    public class LoginByGrant : ICustomGrantValidator
    {
        private readonly ApplicationUserManager _userManager;

        public string GrantType => "loginBy";

        public LoginByGrant(ApplicationUserManager userManager)
        {
            _userManager = userManager;
        }     

        public async Task<CustomGrantValidationResult> ValidateAsync(ValidatedTokenRequest request)
        {

            var userId = Guid.Parse(request.Raw.Get("user_id"));

            var user = await _userManager.FindByIdAsync(userId);

            if (user == null)
                return await Task.FromResult<CustomGrantValidationResult>(new CustomGrantValidationResult("user not exist"));

            var userClaims = await _userManager.GetClaimsAsync(user.Id);

            return
                await Task.FromResult<CustomGrantValidationResult>(new CustomGrantValidationResult(user.Id.ToString(), "custom", userClaims));

        }
    }

then add this custom grant in identity startup class

    factory.CustomGrantValidators.Add(
                        new Registration<ICustomGrantValidator>(resolver => new LoginByGrant(ApplicaionUserManager)));

and finally in your api

      public async Task<IHttpActionResult> LoginBy(Guid userId)
       {
        var tokenClient = new TokenClient(Constants.TokenEndPoint, Constants.ClientId, Constants.Secret);

        var payload = new { user_id = userId.ToString() };

        var result = await tokenClient.RequestCustomGrantAsync("loginBy", "customScope", payload);

        if (result.IsError)
            return Ok(result.Json);

        return Ok(new { access_token = result.AccessToken, expires_in = result.ExpiresIn});
       }

this is for identityServer3 but for identityServer4 it is pretty similar