Supabase Auth with ASP.NET

May 09, 2024 ·

1 Min Read

Start with NuGet

First of all, we need some NuGet packages:

System.IdentityModel.Tokens.Jwt
Microsoft.AspNetCore.Authentication.JwtBearer

There’s no need to elaborate, just download them from Visual Studio. They will be useful for the code that follows.

Setup in your project

You can now add this code inside your Program.cs:

// Configure authentication
var supabaseUrl = Environment.GetEnvironmentVariable("SUPABASE_URL")
    ?? builder.Configuration.GetSection("Supabase").GetSection("Url").Value;
var supabaseSignatureStr = Environment.GetEnvironmentVariable("SUPABASE_SIGNATURE")
    ?? builder.Configuration.GetSection("Supabase").GetSection("Signature").Value;

if (supabaseSignatureStr == string.Empty)
    throw new Exception("Supabase signature is empty");

var supabaseSignatureKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(supabaseSignatureStr!));
var validIssuer = supabaseUrl + "/auth/v1";
var validAudiences = new List<string>() { "authenticated" };

builder.Services.AddAuthentication().AddJwtBearer(o =>
{
    o.TokenValidationParameters = new TokenValidationParameters
    {
        ValidateIssuerSigningKey = true,
        IssuerSigningKey = supabaseSignatureKey,
        ValidAudiences = validAudiences,
        ValidIssuer = validIssuer
    };
});

The code is really easy. Nothing fancy. Like you can see, you have to define SUPABASE_URL and SUPABASE_SIGNATURE.

To validate the JWT token coming from Supabase, you need the signing key. You can get it from the SQL Editor of your Supabase project dashboard with the following SQL Query show app.settings.jwt_secret;.