Implement jwks endpoint and add test for it.

This also let to some improvements/cleanups of the other tests and fixtures.

IdentityShroud.Api.Tests/Mappers/KeyMapperTests.cs

@@ -0,0 +1,41 @@
+using System.Security.Cryptography;
+using IdentityShroud.Api.Mappers;
+using IdentityShroud.Core.Contracts;
+using IdentityShroud.Core.Messages;
+using IdentityShroud.Core.Model;
+using IdentityShroud.TestUtils.Substitutes;
+using Microsoft.AspNetCore.WebUtilities;
+
+namespace IdentityShroud.Api.Tests.Mappers;
+
+public class KeyMapperTests
+{
+    private readonly IEncryptionService _encryptionService = EncryptionServiceSubstitute.CreatePassthrough();
+
+    [Fact]
+    public void Test()
+    {
+        // Setup
+        using RSA rsa = RSA.Create(2048);
+
+        RSAParameters parameters = rsa.ExportParameters(includePrivateParameters: false);
+        
+        Key key = new()
+        {
+            Id = new("60bb79cf-4bac-4521-87f2-ac87cc15541f"),
+            CreatedAt = DateTime.UtcNow,
+            Priority = 10,
+        };
+        key.SetPrivateKey(_encryptionService, rsa.ExportPkcs8PrivateKey());
+
+        // Act
+        KeyMapper mapper = new(_encryptionService);
+        JsonWebKey jwk = mapper.KeyToJsonWebKey(key);
+
+        Assert.Equal("RSA", jwk.KeyType);
+        Assert.Equal(key.Id.ToString(), jwk.KeyId);
+        Assert.Equal("sig", jwk.Use);
+        Assert.Equal(parameters.Exponent, WebEncoders.Base64UrlDecode(jwk.Exponent));
+        Assert.Equal(parameters.Modulus, WebEncoders.Base64UrlDecode(jwk.Modulus));
+    }
+}