什麼是符記？
對於來自低信任環境的 API 方法呼叫，Fleet Engine 要求使用由適當服務帳戶簽署的 JSON Web Token (JWT)。信任度低的環境包括智慧型手機和瀏覽器。JWT 會在伺服器上產生，而伺服器是完全信任的環境。系統會為 JWT 簽署、加密，並將其傳遞給用戶端，以便後續的伺服器互動，直到 JWT 到期或不再有效為止。
後端應使用標準的應用程式預設憑證機制，針對 Fleet Engine 進行驗證和授權。請務必使用經過適當服務帳戶簽署的 JWT。如需服務帳戶角色清單，請參閱「Fleet Engine 基礎知識」中的Fleet Engine 服務帳戶角色。
相反地，後端應使用標準的應用程式預設憑證機制，針對 Fleet Engine 進行驗證及授權。
如要進一步瞭解 JSON Web Token，請參閱 Fleet Engine 重點中的「JSON Web Token」。
用戶端如何取得權杖？
駕駛員或消費者使用適當的驗證憑證登入應用程式後，從該裝置發出的任何更新都必須使用適當的授權權杖，以便向 Fleet Engine 傳達應用程式的權限。
身為開發人員，您的用戶端實作項目應提供以下功能：
- 從伺服器擷取 JSON Web Token。
- 在權杖到期前重複使用，盡量減少權杖重新整理次數。
- 在權杖到期時重新整理。
GMTDAuthorization 通訊協定會根據 GMTD AuthorizationContext 物件，在位置更新時間擷取 JSON Web 權杖。SDK 必須將權杖與更新資訊封裝，才能傳送至 Fleet Engine。請確認伺服器端實作項目可以在初始化 SDK 之前發出權杖。
如要進一步瞭解 Fleet Engine 所需的符記，請參閱 Fleet Engine 的「發出 JSON Web Token」一文。
providerID 與 Google Cloud 專案的專案 ID 相同。如要瞭解如何設定 Google Cloud 專案，請參閱「建立 Fleet Engine 專案」一文。
驗證權杖擷取器範例
以下範例實作授權權杖提供者：
Swift
/*
* SampleAccessTokenProvider.swift
*/
import GoogleRidesharingConsumer
private let providerURL = "INSERT_YOUR_TOKEN_PROVIDER_URL"
class SampleAccessTokenProvider: NSObject, GMTCAuthorization {
private struct AuthToken {
// The cached trip token.
let token: String
// Keep track of when the token expires for caching.
let expiration: TimeInterval
// Keep track of the trip ID the cached token is for.
let tripID: String
}
enum AccessTokenError: Error {
case missingAuthorizationContext
case missingData
}
private var authToken: AuthToken?
func fetchToken(
with authorizationContext: GMTCAuthorizationContext?,
completion: @escaping GMTCAuthTokenFetchCompletionHandler
) {
// Get the trip ID from the authorizationContext. This is set by the Consumer SDK.
guard let authorizationContext = authorizationContext else {
completion(nil, AccessTokenError.missingAuthorizationContext)
return
}
let tripID = authorizationContext.tripID
// If appropriate, use the cached token.
if let authToken = authToken,
authToken.expiration > Date.now.timeIntervalSince1970 && authToken.tripID == tripID
{
completion(authToken.token, nil)
return
}
// Otherwise, try to fetch a new token from your server.
let request = URLRequest(url: URL(string: providerURL))
let task = URLSession.shared.dataTask(with: request) { [weak self] data, _, error in
guard let strongSelf = self else { return }
guard error == nil else {
completion(nil, error)
return
}
// Replace the following key values with the appropriate keys based on your
// server's expected response.
let tripTokenKey = "TRIP_TOKEN_KEY"
let tokenExpirationKey = "TOKEN_EXPIRATION"
guard let data = data,
let fetchData = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
let token = fetchData[tripTokenKey] as? String,
let expiration = fetchData[tokenExpirationKey] as? Double
else {
completion(nil, AccessTokenError.missingData)
return
}
strongSelf.authToken = AuthToken(token: token, expiration: expiration, tripID: tripID)
completion(token, nil)
}
task.resume()
}
}
Objective-C
/*
* SampleAccessTokenProvider.h
*/
#import <Foundation/Foundation.h>
#import <GoogleRidesharingConsumer/GoogleRidesharingConsumer.h>
NS_ASSUME_NONNULL_BEGIN
@interface SampleAccessTokenProvider : NSObject <GMTCAuthorization>
@end
NS_ASSUME_NONNULL_END
/*
* SampleAccessTokenProvider.m
*/
#import "SampleAccessTokenProvider.h"
#import "GoogleRidesharingConsumer/GoogleRidesharingConsumer.h"
static NSString *const PROVIDER_URL = @"INSERT_YOUR_TOKEN_PROVIDER_URL";
// SampleAccessTokenProvider.m
@implementation SampleAccessTokenProvider {
// The cached token with claims to the current trip.
NSString *_cachedTripToken;
// Keep track of the Trip ID the cached token is for.
NSString *_lastKnownTripID;
// Keep track of when tokens expire for caching.
NSTimeInterval _tokenExpiration;
}
- (void)fetchTokenWithContext:(nullable GMTCAuthorizationContext *)authorizationContext
completion:(nonnull GMTCAuthTokenFetchCompletionHandler)completion {
// Get the trip ID from the authorizationContext. This is set by the Consumer SDK.
NSString *tripID = authorizationContext.tripID;
// Clear cached trip token if trip ID has changed.
if (![_lastKnownTripID isEqual:tripID]) {
_tokenExpiration = 0.0;
_cachedTripToken = nil;
}
_lastKnownTripID = tripID;
// Clear cached tripToken if it has expired.
if ([[NSDate date] timeIntervalSince1970] > _tokenExpiration) {
_cachedTripToken = nil;
}
// If appropriate, use the cached token.
if (_cachedTripToken) {
completion(_cachedTripToken, nil);
return;
}
// Otherwise, try to fetch a new token from your server.
NSURL *requestURL = [NSURL URLWithString:PROVIDER_URL];
NSMutableURLRequest *request =
[[NSMutableURLRequest alloc] initWithURL:requestURL];
request.HTTPMethod = @"GET";
// Replace the following key values with the appropriate keys based on your
// server's expected response.
NSString *tripTokenKey = @"TRIP_TOKEN_KEY";
NSString *tokenExpirationKey = @"TOKEN_EXPIRATION";
__weak typeof(self) weakSelf = self;
void (^handler)(NSData *_Nullable data, NSURLResponse *_Nullable response,
NSError *_Nullable error) =
^(NSData *_Nullable data, NSURLResponse *_Nullable response, NSError *_Nullable error) {
typeof(self) strongSelf = weakSelf;
if (error) {
completion(nil, error);
return;
}
NSError *JSONError;
NSMutableDictionary *JSONResponse =
[NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&JSONError];
if (JSONError) {
completion(nil, JSONError);
return;
} else {
// Sample code only. No validation logic.
id expirationData = JSONResponse[tokenExpirationKey];
if ([expirationData isKindOfClass:[NSNumber class]]) {
NSTimeInterval expirationTime = ((NSNumber *)expirationData).doubleValue;
strongSelf->_tokenExpiration = [[NSDate date] timeIntervalSince1970] + expirationTime;
}
strongSelf->_cachedTripToken = JSONResponse[tripTokenKey];
completion(JSONResponse[tripTokenKey], nil);
}
};
NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSession *mainQueueURLSession =
[NSURLSession sessionWithConfiguration:config delegate:nil
delegateQueue:[NSOperationQueue mainQueue]];
NSURLSessionDataTask *task = [mainQueueURLSession dataTaskWithRequest:request completionHandler:handler];
[task resume];
}
@end