Implement jwks endpoint and add test for it.

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

IdentityShroud.Api/Apis/DTO/JsonWebKey.cs

@@ -0,0 +1,41 @@
+using System.Text.Json.Serialization;
+
+namespace IdentityShroud.Core.Messages;
+
+// https://www.rfc-editor.org/rfc/rfc7517.html
+
+
+public class JsonWebKey
+{
+    [JsonPropertyName("kty")]
+    public string KeyType { get; set; } = "RSA";
+    
+    // Common values sig(nature) enc(ryption)
+    [JsonPropertyName("use")]
+    public string? Use { get; set; } = "sig"; // "sig" for signature, "enc" for encryption
+    
+    // Per standard this field is optional, commented out for now as it seems not 
+    // have any good use in an identity server. Anyone validating tokens should use
+    // the algorithm specified in the header of the token.
+    // [JsonPropertyName("alg")]
+    // public string? Algorithm { get; set; } = "RS256";
+    
+    [JsonPropertyName("kid")]
+    public required string KeyId { get; set; }
+    
+    // RSA Public Key Components
+    [JsonPropertyName("n")]
+    public required string Modulus { get; set; }
+    
+    [JsonPropertyName("e")]
+    public required string Exponent { get; set; }
+    
+    // Optional fields
+    [JsonPropertyName("x5c")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public List<string>? X509CertificateChain { get; set; }
+    
+    [JsonPropertyName("x5t")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? X509CertificateThumbprint { get; set; }    
+}

IdentityShroud.Api/Apis/DTO/JsonWebKeySet.cs

@@ -0,0 +1,9 @@
+using System.Text.Json.Serialization;
+
+namespace IdentityShroud.Core.Messages;
+
+public class JsonWebKeySet
+{
+    [JsonPropertyName("keys")]
+    public List<JsonWebKey> Keys { get; set; } = new List<JsonWebKey>();
+}