Add SPKI-based certificate pinning support

Package.swift

@@ -44,6 +44,7 @@ let package = Package(
         .package(url: "https://github.com/apple/swift-atomics.git", from: "1.0.2"),
         .package(url: "https://github.com/apple/swift-algorithms.git", from: "1.0.0"),
         .package(url: "https://github.com/apple/swift-distributed-tracing.git", from: "1.3.0"),
+        .package(url: "https://github.com/apple/swift-crypto.git", from: "4.2.0"),
         .package(url: "https://github.com/apple/swift-configuration.git", from: "1.0.0"),
     ],
     targets: [
@@ -70,6 +71,7 @@ let package = Package(
                 .product(name: "NIOTransportServices", package: "swift-nio-transport-services"),
                 .product(name: "Atomics", package: "swift-atomics"),
                 .product(name: "Algorithms", package: "swift-algorithms"),
+                .product(name: "Crypto", package: "swift-crypto"),
                 .product(name: "Configuration", package: "swift-configuration"),
                 // Observability support
                 .product(name: "Logging", package: "swift-log"),

Sources/AsyncHTTPClient/AsyncAwait/HTTPClientRequest+Prepared.swift

@@ -42,6 +42,7 @@ extension HTTPClientRequest {
         var head: HTTPRequestHead
         var body: Body?
         var tlsConfiguration: TLSConfiguration?
+        var tlsPinning: SPKIPinningConfiguration?
     }
 }
 
@@ -82,7 +83,8 @@ extension HTTPClientRequest.Prepared {
                 headers: headers
             ),
             body: request.body.map { .init($0) },
-            tlsConfiguration: request.tlsConfiguration
+            tlsConfiguration: request.tlsConfiguration,
+            tlsPinning: request.tlsPinning
         )
     }
 }

Sources/AsyncHTTPClient/AsyncAwait/HTTPClientRequest.swift

@@ -53,6 +53,9 @@ public struct HTTPClientRequest: Sendable {
     /// Request-specific TLS configuration, defaults to no request-specific TLS configuration.
     public var tlsConfiguration: TLSConfiguration?
 
+    /// Optional SPKI pinning configuration for TLS certificate validation.
+    public var tlsPinning: SPKIPinningConfiguration?
+
     public init(url: String) {
         self.url = url
         self.method = .GET

Sources/AsyncHTTPClient/AsyncAwait/Transaction.swift

@@ -173,6 +173,7 @@ final class Transaction:
 extension Transaction: HTTPSchedulableRequest {
     var poolKey: ConnectionPool.Key { self.request.poolKey }
     var tlsConfiguration: TLSConfiguration? { self.request.tlsConfiguration }
+    var tlsPinning: SPKIPinningConfiguration? { self.request.tlsPinning }
     var requiredEventLoop: EventLoop? { nil }
 
     func requestWasQueued(_ scheduler: HTTPRequestScheduler) {