refactor: Move payload deseriaisation to decoder

Author: kylef

Sources/JWT/CompactJSONDecoder.swift

@@ -1,3 +1,5 @@
+import Foundation
+
 class CompactJSONDecoder: JSONDecoder {
   override func decode<T>(_ type: T.Type, from data: Data) throws -> T where T : Decodable {
     guard let string = String(data: data, encoding: .ascii) else {
@@ -14,4 +16,17 @@ class CompactJSONDecoder: JSONDecoder {
 
     return try super.decode(type, from: decoded)
   }
+
+  func decode(from string: String) throws -> Payload {
+    guard let decoded = base64decode(string) else {
+      throw InvalidToken.decodeError("Payload is not correctly encoded as base64")
+    }
+
+    let object = try JSONSerialization.jsonObject(with: decoded)
+    guard let payload = object as? Payload else {
+      throw InvalidToken.decodeError("Invalid payload")
+    }
+
+    return payload
+  }
 }

Sources/JWT/Decode.swift

@@ -90,22 +90,13 @@ func load(_ jwt: String) throws -> (header: JOSEHeader, payload: ClaimSet, signa
 
   let decoder = CompactJSONDecoder()
   let header = try decoder.decode(JOSEHeader.self, from: headerSegment)
-
-  let payloadData = base64decode(payloadSegment)
-  if payloadData == nil {
-    throw InvalidToken.decodeError("Payload is not correctly encoded as base64")
-  }
-
-  let payload = (try? JSONSerialization.jsonObject(with: payloadData!, options: JSONSerialization.ReadingOptions(rawValue: 0))) as? Payload
-  if payload == nil {
-    throw InvalidToken.decodeError("Invalid payload")
-  }
+  let payload = try decoder.decode(from: payloadSegment)
 
   guard let signature = base64decode(signatureSegment) else {
     throw InvalidToken.decodeError("Signature is not correctly encoded as base64")
   }
 
-  return (header: header, payload: ClaimSet(claims: payload!), signature: signature, signatureInput: signatureInput)
+  return (header: header, payload: ClaimSet(claims: payload), signature: signature, signatureInput: signatureInput)
 }
 
 // MARK: Signature Verification