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SwiftJWT

An implementation of JSON Web Token using Swift. JWTs offer a lightweight and compact format for transmitting information between parties, and the information can be verified and trusted due to JWTs being digitally signed.

For more information on JSON Web Tokens, their use cases and how they work, we recommend visiting jwt.io.

Reminder: JWTs sent as JWS do not encrypt data, so never send anything sensitive or confidential in a JWT. This library does not currently support JWE.

Swift version

The latest version of Swift-JWT requires Swift 4.0 or later. You can download this version of the Swift binaries by following this link. Compatibility with other Swift versions is not guaranteed.

Usage

Swift Package Manager

Add dependencies

Add the Swift-JWT package to the dependencies within your application’s Package.swift file. Substitute "x.x.x" with the latest Swift-JWT release.

.package(url: "https://github.com/IBM-Swift/Swift-JWT.git", from: "x.x.x")

Add SwiftJWT to your target’s dependencies:

.target(name: "example", dependencies: ["SwiftJWT"]),

Import package

import SwiftJWT

Cocoapods

To include Swift-JWT in a project using CocoaPods, add SwiftJWT to your Podfile:

pod 'SwiftJWT'

Getting Started

The JWT model

In its compact form, a JSON Web Tokens consist of three sections of Base64Url encoded JSON, separated by dots (.).
These section are: Headers, Claims and the Signature. Therefore, a JWT typically looks like the following: xxxxx.yyyyy.zzzzz

The Header struct contains the fields of the JSON Web Token header as defined by RFC7515.
The typ header will default to JWT. The alg header will be set to the algorithm name when you sign the JWT.
The other Header fields can be set when initializing the Header or by changing them directly on the Header object.

let myHeader = Header(kid: "KeyID1")

Claims

Claims are statements about an entity (typically, the user) and additional data. The Claims are defined by creating a Swift type that conforms to the Claims protocol. The fields of this type represent the information that will be shared using the JWT.

A list of recommended claims is defined in RFC7519.

struct MyClaims: Claims {
    let iss: String
    let sub: String
    let exp: Date
    let admin: Bool
}
let myClaims = MyClaims(iss: "Kitura", sub: "John", exp: Date(timeIntervalSinceNow: 3600), admin: true)
ClaimsExamples

This library includes some example Claims structs as defined by their online specifications:

JWT

The JWT struct represents the Header and Claims of a JSON Web Token.
You can initialize a JWT by decoding a JWT String, or by providing the JWT Header and Claims.

let myJWT = JWT(header: myHeader, claims: myClaims)

Signing and Verifying JSON web tokens

Creating the RSA public and private keys

To sign and verify a JWT using an RSA algorithm, you must provide a public and private key. This could be the contents of a .key file generated via the following Terminal commands:

$ ssh-keygen -t rsa -b 4096 -f privateKey.key
# Don't add a passphrase
$ openssl rsa in privateKey.key -pubout -outform PEM -out privateKey.key.pub

This will create a public and private key pair on your system, and the contents of the private key can be passed into a Swift variable using the following code:

let privateKeyPath = URL(fileURLWithPath: getAbsolutePath(relativePath: "/path/to/privateKey.key"))
let privateKey: Data = try Data(contentsOf: privateKeyPath, options: alwaysMapped)
let publicKeyPath = URL(fileURLWithPath: getAbsolutePath(relativePath: "/path/to/publicKey.key"))
let publicKey: Data = try Data(contentsOf: publicKeyPath, options: alwaysMapped)

Sign a JWT using a JWTSigner

The struct JWTSigner contains the algorithms that can be used to sign a JWT.

Initialize a JWTSigner using the static function corresponding to the desired RSA algorithm:

let jwtSigner = JWTSigner.rs256(privateKey: privateKey)

To generate a signed JWT string, call the sign function on your JWT instance, passing in a JWTSigner:

let signedJWT = try myJWT.sign(using: jwtSigner)

The resulting signedJWT will be a String of the form:

<encoded header>.<encoded claims>.<signature>

Note: The sign function sets the alg (algorithm) field of the header.

Verify a JWT using JWTVerifier

The struct JWTVerifier contains the algorithms that can be used to verify a JWT.

Initialize a JWTVerifier using the static function corresponding to the desired RSA algorithm:

let jwtVerifier = JWTVerifier.rs256(publicKey: publicKey)

To verify a signed JWT string, call the static verify function, passing in your JWT string and the JWTVerifier:

let verified = JWT<MyClaims>.verify(signedJWT, using: jwtVerifier)

The verified field will be a bool that is true if the signature is verified.

Supported Algorithms

The supported algorithms for signing and verifying JWTs are:

  • RS256 - RSASSA-PKCS1-v1_5 using SHA-256
  • RS384 - RSASSA-PKCS1-v1_5 using SHA-384
  • RS512 - RSASSA-PKCS1-v1_5 using SHA-512
  • HS256 - HMAC using using SHA-256
  • HS384 - HMAC using using SHA-384
  • HS512 - HMAC using using SHA-512
  • none - Don’t sign or verify the JWT

Validate claims

The validateClaims function validates the Standard Date claims of a JWT instance. The following claims are validated if they are present in the Claims object:

  • exp (expiration date)
  • nbf (not before date)
  • iat (issued at date)

The method returns ValidateClaimsResult - an struct that list the various reasons for validation failure. If the validation succeeds ValidateClaimsResult.success is returned.

let validationResult = verified.validateClaims()
if validationResult != .success {
    print("Claims validation failed: ", validationResult)
}

Decode a JWT from a JWT string

A JWT struct can be initialized from a JWT string. If a JWTVerifier is provided it will be used to verify the signature before initialization

let newJWT = try JWT<MyClaims>(jwtString: signedJWT, jwtVerifier: jwtVerifier)

JWTEncoder and JWTDecoder

The JWTEncoder and JWTDecoder classes encode and decode JWT Strings using the same API as JSONEncoder and JSONDecoder:

 let jwtEncoder = JWTEncoder(jwtSigner: jwtSigner)
 let jwtString = try jwtEncoder.encodeToString(myJWT)

 let jwtDecoder = JWTDecoder(jwtVerifier: jwtVerifier)
 let jwt = try jwtDecoder.decode(JWT<MyClaims>.self, fromString: jwtString)

Because JWTEncoder and JWTDecoder conform to KituraContract’s BodyEncoder and BodyDecoder protocols, they can be used as a custom coder in Codable routes for sending and receiving JWTs:

 router.encoders[MediaType(type: .application, subType: "jwt")] = { return jwtEncoder }
 router.decoders[MediaType(type: .application, subType: "jwt")] = { return jwtDecoder }

This allows for the use of JWT’s in information exchange. By sending and receiving JWT’s you can ensure the sending is who they say they are and verify the content hasn’t been tampered with.

API Documentation

For more information visit our [API reference](https://ibm-swift.github.io/Swift-JWT/index.html.

Community

We love to talk server-side Swift, and Kitura. Join our Slack to meet the team!

License

This library is licensed under Apache 2.0. Full license text is available in LICENSE.