Reworked encryption to use less heap allocated buffers for secrets.

Also some work on plugin system.

IdentityShroud.Core/Security/Jwt/IJwtSignatureProvider.cs

@@ -1,26 +0,0 @@
-using System.Text.Json;
-
-namespace IdentityShroud.Core;
-
-public interface IJwtSignatureProvider : IDisposable
-{
-    /*
-        Of the signature and MAC algorithms specified in JSON Web Algorithms
-        [JWA], only HMAC SHA-256 ("HS256") and "none" MUST be implemented by
-        conforming JWT implementations.  It is RECOMMENDED that
-        implementations also support RSASSA-PKCS1-v1_5 with the SHA-256 hash
-        algorithm ("RS256") and ECDSA using the P-256 curve and the SHA-256
-        hash algorithm ("ES256").  Support for other algorithms and key sizes
-        is OPTIONAL.
-     */
-
-    void WriteJwtHeaderFields(Utf8JsonWriter writer);
-    /// <summary>
-    /// Length of the binary signature in bytes. 
-    /// </summary>
-    /// <returns></returns>
-    int GetSignatureLength();
-
-    void CalculateSignature(ReadOnlySpan<byte> jwt, Span<byte> signatureOut);
-    
-}