aws-appsync-realtime-client-ios/AppSyncRealTimeClient/Interceptor/OIDCAuthInterceptor.swift

//
// Copyright Amazon.com Inc. or its affiliates.
// All Rights Reserved.
//
// SPDX-License-Identifier: Apache-2.0
//

import Foundation

public class OIDCAuthInterceptor: AuthInterceptor {

    let authProvider: OIDCAuthProvider

    public init(_ authProvider: OIDCAuthProvider) {
        self.authProvider = authProvider
    }

    public func interceptMessage(
        _ message: AppSyncMessage,
        for endpoint: URL,
        completion: @escaping (AppSyncMessage) -> Void
    ) {
        guard let host = endpoint.host else {
            completion(message)
            return
        }

        guard case .subscribe = message.messageType else {
            completion(message)
            return
        }

        authProvider.getLatestAuthToken { result in
            let signedMessage = self.signMessage(message, with: result, host: host)
            completion(signedMessage)
            return
        }
    }


    public func interceptConnection(
        _ request: AppSyncConnectionRequest,
        for endpoint: URL,
        completion: @escaping (AppSyncConnectionRequest) -> Void
    ) {

        guard let host = endpoint.host else {
            completion(request)
            return
        }

        authProvider.getLatestAuthToken { result in
            let signedRequest = self.signRequest(request, with: result, host: host)
            completion(signedRequest)
            return
        }
    }

    private func signMessage(
        _ message: AppSyncMessage,
        with tokenResult: Result<String, Error>,
        host: String
    ) -> AppSyncMessage {
            let jwtToken: String
            switch tokenResult {
            case .success(let token):
                jwtToken = token
            case .failure:
                return message
            }
            let authHeader = UserPoolsAuthenticationHeader(token: jwtToken, host: host)
            var payload = message.payload ?? AppSyncMessage.Payload()
            payload.authHeader = authHeader

            return AppSyncMessage(
                id: message.id,
                payload: payload,
                type: message.messageType
            )
        }

    private func signRequest(
        _ request: AppSyncConnectionRequest,
        with tokenResult: Result<String, Error>,
        host: String
    ) -> AppSyncConnectionRequest {
            let jwtToken: String
            switch tokenResult {
            case .success(let token):
                jwtToken = token
            case .failure:
                // A user that is not signed in should receive an unauthorized error from
                // the connection attempt. This code achieves this by always creating a valid
                // request to AppSync even when the token cannot be retrieved. The request sent
                // to AppSync will receive a response indicating the request is unauthorized.
                // If we do not use empty token string and perform the remaining logic of the
                // request construction then it will fail request validation at AppSync before
                // the authorization check, which ends up being propagated back to the caller
                // as a "bad request". Example of bad requests are when the header and payload
                // query strings are missing or when the data is not base64 encoded.
                jwtToken = ""
            }

            let authHeader = UserPoolsAuthenticationHeader(token: jwtToken, host: host)
            let base64Auth = AppSyncJSONHelper.base64AuthenticationBlob(authHeader)

            let payloadData = SubscriptionConstants.emptyPayload.data(using: .utf8)
            let payloadBase64 = payloadData?.base64EncodedString()

            guard var urlComponents = URLComponents(url: request.url, resolvingAgainstBaseURL: false) else {
                return request
            }
            let headerQuery = URLQueryItem(name: RealtimeProviderConstants.header, value: base64Auth)
            let payloadQuery = URLQueryItem(name: RealtimeProviderConstants.payload, value: payloadBase64)
            urlComponents.queryItems = [headerQuery, payloadQuery]
            guard let url = urlComponents.url else {
                return request
            }
            let signedRequest = AppSyncConnectionRequest(url: url)
            return signedRequest
        }

    // MARK: Deprecated methods
    // Keeping these methods for backward compatibility

    public func interceptMessage(
        _ message: AppSyncMessage,
        for endpoint: URL
    ) -> AppSyncMessage {

        guard let host = endpoint.host else {
            return message
        }

        guard case .subscribe = message.messageType else {
            return message
        }
        let result = authProvider.getLatestAuthToken()
        let signedMessage = signMessage(message, with: result, host: host)
        return signedMessage
    }

    public func interceptConnection(
        _ request: AppSyncConnectionRequest,
        for endpoint: URL
    ) -> AppSyncConnectionRequest {

        guard let host = endpoint.host else {
            return request
        }

        let result = authProvider.getLatestAuthToken()
        let signedRequest = signRequest(request, with: result, host: host)
        return signedRequest
    }
}

/// Authentication header for user pool based auth
private class UserPoolsAuthenticationHeader: AuthenticationHeader {
    let authorization: String

    init(token: String, host: String) {
        self.authorization = token
        super.init(host: host)
    }

    private enum CodingKeys: String, CodingKey {
        case authorization = "Authorization"
    }

    override func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(authorization, forKey: .authorization)
        try super.encode(to: encoder)
    }
}