Configures Tesla OpenID Connect authentication

Implements authentication against the Tesla Fleet API using OpenID Connect.

Uses a custom OIDC configuration manager to override the token endpoint.
Configures authentication services and adds required scopes and parameters.
Adds endpoints for application registration and token retrieval during development.

Source/ProofOfConcept/Utilities/TeslaOIDCConfigurationManager.cs

@@ -0,0 +1,31 @@
+using Microsoft.IdentityModel.Protocols;
+using Microsoft.IdentityModel.Protocols.OpenIdConnect;
+
+namespace ProofOfConcept.Utilities;
+
+using Microsoft.IdentityModel.Protocols;
+using Microsoft.IdentityModel.Protocols.OpenIdConnect;
+
+public sealed class TeslaOIDCConfigurationManager : IConfigurationManager<OpenIdConnectConfiguration>
+{
+    private readonly IConfigurationManager<OpenIdConnectConfiguration> _inner;
+    private readonly string _tokenEndpointOverride;
+
+    // No HttpClient/ServiceProvider needed — uses default retriever internally
+    public TeslaOIDCConfigurationManager(string metadataAddress, string tokenEndpointOverride)
+    {
+        _tokenEndpointOverride = tokenEndpointOverride;
+        _inner = new ConfigurationManager<OpenIdConnectConfiguration>(
+            metadataAddress,
+            new OpenIdConnectConfigurationRetriever());
+    }
+
+    public async Task<OpenIdConnectConfiguration> GetConfigurationAsync(CancellationToken cancel)
+    {
+        var cfg = await _inner.GetConfigurationAsync(cancel).ConfigureAwait(false);
+        cfg.TokenEndpoint = _tokenEndpointOverride; // <-- required by Tesla
+        return cfg;
+    }
+
+    public void RequestRefresh() => _inner.RequestRefresh();
+}