SMS using Twilio Rest API in ASP.NET Core

A couple of weeks ago I went over using email in ASP.NET Core which left the provided MessageService class half implemented.  This post is going to cover the implementation of the other MessageService function that is used to send SMS as part of two-factor authentication.

View

In Views/Manage/Index.cshtml uncomment the following to enable the UI bit associated with phone numbers.

@(Model.PhoneNumber ?? "None")
    @if (Model.PhoneNumber != null)
    {
        <br />
        <text>[&nbsp;&nbsp;<a asp-controller="Manage" asp-action="AddPhoneNumber">Change</a>&nbsp;&nbsp;]</text>
        <form asp-controller="Manage" asp-action="RemovePhoneNumber" method="post" role="form">
            [<button type="submit" class="btn-link">Remove</button>]
        </form>
    }
    else
    {
        <text>[&nbsp;&nbsp;<a asp-controller="Manage" asp-action="AddPhoneNumber">Add</a>&nbsp;&nbsp;]</text>
    }

And this as well.

@if (Model.TwoFactor)
    {
        <form asp-controller="Manage" asp-action="DisableTwoFactorAuthentication" method="post" class="form-horizontal" role="form">
            Enabled [<button type="submit" class="btn-link">Disable</button>]
        </form>
    }
    else
    {
        <form asp-controller="Manage" asp-action="EnableTwoFactorAuthentication" method="post" class="form-horizontal" role="form">
            [<button type="submit" class="btn-link">Enable</button>] Disabled
        </form>
    }

Twilio

I spend a lot of time trying to find a services that allows sending of SMS for free and had zero luck. I ended up going with  Twilio as they do provide free messaging with their trial account. The usage section of the web site will make it looking like you will be changed, but that is just to provide an idea of what the service would cost and will not actually be charged.

Storing Configuration

Just as a couple of weeks ago for EmailSetting I created a SmsSettings class that will be loaded from user secrets in the StartUp class of the application. For more details on general configuration in ASP.NET Core check out this post and then this post for more details on user secrets. The following is my SMS settings class.

public class SmsSettings
{
    public string Sid { get; set; }
    public string Token { get; set; }
    public string BaseUri { get; set; }
    public string RequestUri { get; set; }
    public string From { get; set; }
}

And this is the config file looks like with the curly braces needed to be replace with values from your Twilio account. For example if your Twilio phone number was 15554447777 then the from line would be: “From”: “+15554447777”

{
  "SmsSettings": {
    "Sid": "{TwilioAccountSid}",
    "Token": "{TwilioAuthToken}",
    "BaseUri": "https://api.twilio.com",
    "RequestUri": "/2010-04-01/Accounts/{TwilioAccountSid}/Messages.json",
    "From": "+{TwilioPhoneNumber}"
  }
}

Then in ConfigureServices function of Startup.cs add a reference to the SmsSettings class to make it available using dependency injection.

services.Configure<SmsSettings>(Configuration.GetSection("SmsSettings"));

Message Services

In Services/MessageService.cs there is an empty implementation for sending SMS base on ISmsSender which defines a single SendSmsAsync function which is called when the application wants to send a SMS.

Add a constructor to the class if it doesn’t already have one so that the SmsSettings can be injected by the framework and add a field to store the settings in. I have removed the email related items from the constructor but you can look at this post if you want to include the email related bits a well.

private readonly SmsSettings _smsSettings;

public AuthMessageSender(IOptions<SmsSettings> smsSettings)
{
    _smsSettings = smsSettings.Value;
}

Then the SendSmsAsync function which uses the HttpClient with basic authentication and form url encoded content to make a post request to the Twilio API looks like the following.

public async Task SendSmsAsync(string number, string message)
{
    using (var client = new HttpClient { BaseAddress = new Uri(_smsSettings.BaseUri) })
    {
        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic",
            Convert.ToBase64String(Encoding.ASCII.GetBytes($"{_smsSettings.Sid}:{_smsSettings.Token}")));

        var content = new FormUrlEncodedContent(new[]
        {
            new KeyValuePair<string, string>("To",$"+{number}"),
            new KeyValuePair<string, string>("From", _smsSettings.From),
            new KeyValuePair<string, string>("Body", message)
        });

        await client.PostAsync(_smsSettings.RequestUri, content).ConfigureAwait(false);
    }
}

Now you application is capable of sending SMS.

ASP.NET Docs

As I was writing this I came across Rick Anderson’s post in the official docs that covers two-factor authentication. I highly recommend you read Rick’s post as he covers the UI portion in more depth than I did. Another note Rick is using the Twilio helper client were I am using the HttpClient in order to maintain dnxcore50 compatibility.