A basic JWT parser for Swift that doesn't do any validation.

JWT.swift

import Foundation


extension Data {
	/// JWT strips the padding off the end of the base64 string
	fileprivate init?(jwtPart: String) {
		var paddingCount = 4 - jwtPart.count % 4
		if paddingCount == 4 {
			paddingCount = 0
		}
		
		let padding = String(repeating: "=", count: paddingCount)
		
		self.init(base64Encoded: jwtPart + padding)
	}
}


// this is a very simplified JWT parser that does not do any actual validation
// we just want to pull the expiration data out of our tokens
// the services will actually validate these
struct JWT {
	enum Error: Swift.Error {
		case wrongNumberOfComponents
		case invalidBase64Content
	}
	
	var header: Data
	var payload: Data
	var signiture: String
	
	init(_ token: String) throws {
		let parts = token.components(separatedBy: ".")
		guard parts.count == 3 else { throw Error.wrongNumberOfComponents }
		
		guard let header = Data(jwtPart: parts[0]) else { throw Error.invalidBase64Content }
		self.header = header
		
		guard let payload = Data(jwtPart: parts[1]) else { throw Error.invalidBase64Content }
		self.payload = payload
		
		signiture = parts[2]
	}
}

struct JWTPayload: Codable {
	var iat: Date
	var exp: Date
	
	func isValid() -> Bool {
		return exp.timeIntervalSinceNow > 0
	}
	
	public init(from decoder: Decoder) throws {
		let container = try decoder.container(keyedBy: CodingKeys.self)
		
		iat = try Date(timeIntervalSince1970: container.decode(TimeInterval.self, forKey: .iat))
		exp = try Date(timeIntervalSince1970: container.decode(TimeInterval.self, forKey: .exp))
	}
}