Merge pull request OAuthSwift#647 from MrWoWander/pkce

Code verifier & code challenge generator for working with PKCE

Package.swift

@@ -37,3 +37,8 @@ let package = Package(
         .testTarget(name: "OAuthSwiftTests", dependencies: ["OAuthSwift", "Erik", "Kanna", "Swifter"], path: "OAuthSwiftTests"),
     ]
 )
+
+#if os(Linux)
+package.dependencies.append(.package(url: "https://github.com/apple/swift-crypto.git", from: "1.0.0"))
+package.targets[0].dependencies.append("Crypto")
+#endif

README.md

@@ -189,8 +189,8 @@ oauthswift = OAuth2Swift(
 )
 oauthswift.accessTokenBasicAuthentification = true
 
-let codeVerifier = base64url("abcd...")
-let codeChallenge = codeChallenge(for: codeVerifier)
+guard let codeVerifier = generateCodeVerifier() else {return}
+guard let codeChallenge = generateCodeChallenge(codeVerifier: codeVerifier) else {return}
 
 let handle = oauthswift.authorize(
     withCallbackURL: "myApp://callback/",
@@ -210,7 +210,6 @@ let handle = oauthswift.authorize(
 
 ```
 
-
 See demo for more examples
 
 ### Handle authorize URL

Sources/Utils.swift

@@ -8,6 +8,12 @@
 
 import Foundation
 
+#if os(Linux)
+import Crypto
+#else
+import CommonCrypto
+#endif
+
 public func generateState(withLength len: Int) -> String {
     let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
     let length = UInt32(letters.count)
@@ -21,3 +27,41 @@ public func generateState(withLength len: Int) -> String {
     }
     return randomString
 }
+
+/// Generating a code verifier for PKCE
+public func generateCodeVerifier() -> String? {
+    var buffer = [UInt8](repeating: 0, count: 32)
+    _ = SecRandomCopyBytes(kSecRandomDefault, buffer.count, &buffer)
+   let codeVerifier = Data(buffer).base64EncodedString()
+        .replacingOccurrences(of: "+", with: "-")
+        .replacingOccurrences(of: "/", with: "_")
+        .replacingOccurrences(of: "=", with: "")
+        .trimmingCharacters(in: .whitespaces)
+
+    return codeVerifier
+}
+
+/// Generating a code challenge for PKCE
+public func generateCodeChallenge(codeVerifier: String?) -> String? {
+    guard let verifier = codeVerifier, let data = verifier.data(using: .utf8) else { return nil }
+
+    #if !os(Linux)
+    var buffer = [UInt8](repeating: 0,  count: Int(CC_SHA256_DIGEST_LENGTH))
+    data.withUnsafeBytes {
+        _ = CC_SHA256($0.baseAddress, CC_LONG(data.count), &buffer)
+    }
+    let hash = Data(buffer)
+    #else
+    let buffer = [UInt8](repeating: 0,  count: SHA256.byteCount)
+    let sha = Array(HMAC<SHA256>.authenticationCode(for: buffer, using: SymmetricKey(size: .bits256)))
+    let hash = Data(sha)
+    #endif
+
+    let challenge = hash.base64EncodedString()
+        .replacingOccurrences(of: "+", with: "-")
+        .replacingOccurrences(of: "/", with: "_")
+        .replacingOccurrences(of: "=", with: "")
+        .trimmingCharacters(in: .whitespaces)
+
+    return challenge
+}