Implement leeway for date validation

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Enhancements
 
 - Allow passing additional headers when encoding a JWT.
+- Allow passing leeway parameter for date checks when verifying a JWT.
 
 
 ## 2.1.0

README.md

@@ -68,6 +68,12 @@ try JWT.decode("eyJh...5w", algorithms: [
 ])
 ```
 
+You might also want to give your iat, exp and nbf checks some kind of leeway to account for skewed clocks. You can do this by passing a `leeway` parameter like this:
+
+```swift
+try JWT.decode("eyJh...5w", algorithm: .hs256("secret".data(using: .utf8)!), leeway: 10)
+```
+
 #### Supported claims
 
 The library supports validating the following claims:

Sources/ClaimSet.swift

@@ -93,18 +93,18 @@ extension ClaimSet {
 // MARK: Validations
 
 extension ClaimSet {
-  public func validate(audience: String? = nil, issuer: String? = nil) throws {
+  public func validate(audience: String? = nil, issuer: String? = nil, leeway: TimeInterval = 0) throws {
     if let issuer = issuer {
       try validateIssuer(issuer)
     }
 
     if let audience = audience {
       try validateAudience(audience)
     }
-
-    try validateExpiary()
-    try validateNotBefore()
-    try validateIssuedAt()
+		
+    try validateExpiary(leeway: leeway)
+    try validateNotBefore(leeway: leeway)
+    try validateIssuedAt(leeway: leeway)
   }
 
   public func validateAudience(_ audience: String) throws {
@@ -131,16 +131,16 @@ extension ClaimSet {
     }
   }
 
-  public func validateExpiary() throws {
-    try validateDate(claims, key: "exp", comparison: .orderedAscending, failure: .expiredSignature, decodeError: "Expiration time claim (exp) must be an integer")
+  public func validateExpiary(leeway: TimeInterval = 0) throws {
+    try validateDate(claims, key: "exp", comparison: .orderedAscending, leeway: (-1 * leeway), failure: .expiredSignature, decodeError: "Expiration time claim (exp) must be an integer")
   }
 
-  public func validateNotBefore() throws {
-    try validateDate(claims, key: "nbf", comparison: .orderedDescending, failure: .immatureSignature, decodeError: "Not before claim (nbf) must be an integer")
+  public func validateNotBefore(leeway: TimeInterval = 0) throws {
+    try validateDate(claims, key: "nbf", comparison: .orderedDescending, leeway: leeway, failure: .immatureSignature, decodeError: "Not before claim (nbf) must be an integer")
   }
 
-  public func validateIssuedAt() throws {
-    try validateDate(claims, key: "iat", comparison: .orderedDescending, failure: .invalidIssuedAt, decodeError: "Issued at claim (iat) must be an integer")
+  public func validateIssuedAt(leeway: TimeInterval = 0) throws {
+    try validateDate(claims, key: "iat", comparison: .orderedDescending, leeway: leeway, failure: .invalidIssuedAt, decodeError: "Issued at claim (iat) must be an integer")
   }
 }
 

Sources/Claims.swift

@@ -1,15 +1,15 @@
 import Foundation
 
-func validateDate(_ payload: Payload, key: String, comparison: ComparisonResult, failure: InvalidToken, decodeError: String) throws {
+func validateDate(_ payload: Payload, key: String, comparison: ComparisonResult, leeway: TimeInterval = 0, failure: InvalidToken, decodeError: String) throws {
   if payload[key] == nil {
     return
   }
 
   guard let date = extractDate(payload: payload, key: key) else {
     throw InvalidToken.decodeError(decodeError)
   }
-
-  if date.compare(Date()) == comparison {
+	
+  if date.compare(Date().addingTimeInterval(leeway)) == comparison {
     throw failure
   }
 }

Sources/Decode.swift

@@ -47,20 +47,20 @@ public enum InvalidToken: CustomStringConvertible, Error {
 
 
 /// Decode a JWT
-public func decode(_ jwt: String, algorithms: [Algorithm], verify: Bool = true, audience: String? = nil, issuer: String? = nil) throws -> ClaimSet {
+public func decode(_ jwt: String, algorithms: [Algorithm], verify: Bool = true, audience: String? = nil, issuer: String? = nil, leeway: TimeInterval = 0) throws -> ClaimSet {
   let (header, claims, signature, signatureInput) = try load(jwt)
 
   if verify {
-    try claims.validate(audience: audience, issuer: issuer)
+    try claims.validate(audience: audience, issuer: issuer, leeway: leeway)
     try verifySignature(algorithms, header: header, signingInput: signatureInput, signature: signature)
   }
 
   return claims
 }
 
 /// Decode a JWT
-public func decode(_ jwt: String, algorithm: Algorithm, verify: Bool = true, audience: String? = nil, issuer: String? = nil) throws -> ClaimSet {
-  return try decode(jwt, algorithms: [algorithm], verify: verify, audience: audience, issuer: issuer)
+public func decode(_ jwt: String, algorithm: Algorithm, verify: Bool = true, audience: String? = nil, issuer: String? = nil, leeway: TimeInterval = 0) throws -> ClaimSet {
+  return try decode(jwt, algorithms: [algorithm], verify: verify, audience: audience, issuer: issuer, leeway: leeway)
 }
 
 /// Decode a JWT

Tests/JWTTests/JWTTests.swift

@@ -279,6 +279,121 @@ class DecodeTests: XCTestCase {
   }
 }
 
+class ValidationTests: XCTestCase {
+  func testClaimJustExpiredWithoutLeeway() {
+    var claims = ClaimSet()
+    claims.expiration = Date().addingTimeInterval(-1)
+
+    do {
+      try claims.validateExpiary()
+      XCTFail("InvalidToken.expiredSignature error should have been thrown.")
+    } catch InvalidToken.expiredSignature {
+      // Correct error thrown
+    } catch {
+      XCTFail("Unexpected error while validating exp claim.")
+    }
+  }
+
+  func testClaimJustNotExpiredWithoutLeeway() {
+    var claims = ClaimSet()
+    claims.expiration = Date().addingTimeInterval(-1)
+
+    do {
+      try claims.validateExpiary(leeway: 2)
+    } catch {
+      XCTFail("Unexpected error while validating exp claim that should be valid with leeway.")
+    }
+  }
+
+  func testNotBeforeIsImmatureSignatureWithoutLeeway() {
+    var claims = ClaimSet()
+    claims.notBefore = Date().addingTimeInterval(1)
+
+    do {
+      try claims.validateNotBefore()
+      XCTFail("InvalidToken.immatureSignature error should have been thrown.")
+    } catch InvalidToken.immatureSignature {
+      // Correct error thrown
+    } catch {
+      XCTFail("Unexpected error while validating nbf claim.")
+    }
+  }
+
+  func testNotBeforeIsValidWithLeeway() {
+    var claims = ClaimSet()
+    claims.notBefore = Date().addingTimeInterval(1)
+
+    do {
+      try claims.validateNotBefore(leeway: 2)
+    } catch {
+      XCTFail("Unexpected error while validating nbf claim that should be valid with leeway.")
+    }
+  }
+
+  func testIssuedAtIsInFutureWithoutLeeway() {
+    var claims = ClaimSet()
+    claims.issuedAt = Date().addingTimeInterval(1)
+
+    do {
+      try claims.validateIssuedAt()
+      XCTFail("InvalidToken.invalidIssuedAt error should have been thrown.")
+    } catch InvalidToken.invalidIssuedAt {
+      // Correct error thrown
+    } catch {
+      XCTFail("Unexpected error while validating iat claim.")
+    }
+  }
+
+  func testIssuedAtIsValidWithLeeway() {
+    var claims = ClaimSet()
+    claims.issuedAt = Date().addingTimeInterval(1)
+
+    do {
+      try claims.validateIssuedAt(leeway: 2)
+    } catch {
+      XCTFail("Unexpected error while validating iat claim that should be valid with leeway.")
+    }
+  }
+}
+
+class IntegrationTests: XCTestCase {
+  func testVerificationFailureWithoutLeeway() {
+    let token = JWT.encode(.none) { builder in
+      builder.issuer = "fuller.li"
+      builder.audience = "cocoapods"
+      builder.expiration = Date().addingTimeInterval(-1) // Token expired one second ago
+      builder.notBefore = Date().addingTimeInterval(1) // Token starts being valid in one second
+      builder.issuedAt = Date().addingTimeInterval(1) // Token is issued one second in the future
+    }
+
+    do {
+      let _ = try JWT.decode(token, algorithm: .none, leeway: 0)
+      XCTFail("InvalidToken error should have been thrown.")
+    } catch is InvalidToken {
+			// Correct error thrown
+    } catch {
+      XCTFail("Unexpected error type while verifying token.")
+    }
+  }
+
+  func testVerificationSuccessWithLeeway() {
+    let token = JWT.encode(.none) { builder in
+      builder.issuer = "fuller.li"
+      builder.audience = "cocoapods"
+      builder.expiration = Date().addingTimeInterval(-1) // Token expired one second ago
+      builder.notBefore = Date().addingTimeInterval(1) // Token starts being valid in one second
+      builder.issuedAt = Date().addingTimeInterval(1) // Token is issued one second in the future
+    }
+
+    do {
+      let _ = try JWT.decode(token, algorithm: .none, leeway: 2)
+      // Due to leeway no error gets thrown.
+    } catch {
+      XCTFail("Unexpected error type while verifying token.")
+    }
+  }
+}
+
 // MARK: Helpers
 
 func assertSuccess(_ decoder: @autoclosure () throws -> Payload, closure: ((Payload) -> Void)? = nil) {