Google APIs は認証に Webサーバ、インストールアプリケーション、クライアントサイドも OAuth 2.0 を使う
まず、 OAuth 2.0 client 証明書を Google API Console で発行してもらう。
次に、 アプリケーションからGoogle 認証サーバにアクセストークン発行を要求し、（ユーザーに）承認されるとトークンが発行される。
このトークンを使って（APIと一緒に要求して）、 Google API にアクセスする。
and sends the token to the Google API that you want to access. For an interactive demonstration of using OAuth 2.0 with Google (including the option to use your own client credentials), experiment with the OAuth 2.0 Playground.
This page gives an overview of the OAuth 2.0 authorization scenarios that Google supports, and provides links to more detailed content. For details about using OAuth 2.0 for authentication, see OpenID Connect.
Note: Given the security implications of getting the implementation correct, we strongly encourage you to use OAuth 2.0 libraries when interacting with Google's OAuth 2.0 endpoints. It is a best practice to use well-debugged code provided by others, and it will help you protect yourself and your users. For more information, see Client libraries.
基本的な流れ（Basic steps）
Oauth 2.9 を使った Google API を使用する際は、全てこのパターンに従う。
Google API から証明書を取得する
Visit the Google API Console to obtain OAuth 2.0 credentials such as a client ID and client secret that are known to both Google and your application. The set of values varies based on what type of application you are building. For example, a JavaScript application does not require a secret, but a web server application does.
Google Authorization Server からアクセストークンを取得する
Before your application can access private data using a Google API, it must obtain an access token that grants access to that API. A single access token can grant varying degrees of access to multiple APIs. A variable parameter called scope controls the set of resources and operations that an access token permits. During the access-token request, your application sends one or more values in the scope parameter.
There are several ways to make this request, and they vary based on the type of application you are building. For example, a JavaScript application might request an access token using a browser redirect to Google, while an application installed on a device that has no browser uses web service requests.
Some requests require an authentication step where the user logs in with their Google account. After logging in, the user is asked whether they are willing to grant the permissions that your application is requesting. This process is called user consent.
If the user grants the permission, the Google Authorization Server sends your application an access token (or an authorization code that your application can use to obtain an access token). If the user does not grant the permission, the server returns an error.
It is generally a best practice to request scopes incrementally, at the time access is required, rather than up front. For example, an app that wants to support purchases should not request Google Wallet access until the user presses the “buy” button; see Incremental authorization.
アクセストークンを Google API に送る
After an application obtains an access token, it sends the token to a Google API in an HTTP authorization header. It is possible to send tokens as URI query-string parameters, but we don't recommend it, because URI parameters can end up in log files that are not completely secure. Also, it is good REST practice to avoid creating unnecessary URI parameter names.
Access tokens are valid only for the set of operations and resources described in the scope of the token request. For example, if an access token is issued for the Google+ API, it does not grant access to the Google Contacts API. You can, however, send that access token to the Google+ API multiple times for similar operations.
必要に応じて、アクセストークンをリフレッシュする
Access tokens have limited lifetimes. If your application needs access to a Google API beyond the lifetime of a single access token, it can obtain a refresh token. A refresh token allows your application to obtain new access tokens.
Note: Save refresh tokens in secure long-term storage and continue to use them as long as they remain valid. Limits apply to the number of refresh tokens that are issued per client-user combination, and per user across all clients, and these limits are different. If your application requests enough refresh tokens to go over one of the limits, older refresh tokens stop working.
Scenarios
ウェブサーバーアプリケーション（Web server applications）
The Google OAuth 2.0 endpoint supports web server applications that use languages and frameworks such as PHP,
Java,
Python, Ruby, and ASP.NET.
The authorization sequence begins when your application redirects a browser to a Google URL; the URL includes query parameters that indicate the type of access being requested. Google handles the user authentication, session selection, and user consent. The result is an authorization code, which the application can exchange for an access token and a refresh token.
The application should store the refresh token for future use and use the access token to access a Google API. Once the access token expires, the application uses the refresh token to obtain a new one.
Your application sends a token request to the Google Authorization Server, receives an authorization code,
exchanges the code for a token, and uses the token to call a Google API endpoint.
For details, see Using OAuth 2.0 for Web Server Applications.
Google OAuth 2.0 endpoint は、PC やモバイル、タブレットのようなデバイスへの組込アプリもサポートしている。この場合、クライアント ID を作成する時に、アプリケーションタイプとして、
Android, Chrome, iOS, Other を選択し、組込アプリを指定する。
クライアント ID 、クライアント secret は、アプリケーションに埋め込んで使用する。
認証作業は Google URL へのリダイレクトで始まる。URLには要求するアスセスタイプを明示するクエリパラメータを付けておく。Google にてユーザー認証を行う。これによりアプリケーションに認証コードを発行し、これをアクセストークン（とリフレッシュトークン）と交換する。
アプリケーション側で、アクセストークンを Google API へのアクセス用として、リフレッシュトークンをトークン更新用として用いる。これは、アクセストークンが失効した際に、アプリケーションはリフレッシュトークンを新しいアクセストークンとの交換に使う。
Your application sends a token request to the Google Authorization Server, receives an authorization code,
exchanges the code for a token, and uses the token to call a Google API endpoint.
詳細は
Using OAuth 2.0 for Installed Applicationsへ
クライアントサイドアプリケーション（Client-side (JavaScript) applications）
Google OAuth 2.0 endpoint はブラウザ上で実行される JavaScript アプリケーションもサポートしている。
The authorization sequence begins when your application redirects a browser to a Google URL; the URL includes query parameters that indicate the type of access being requested. Google handles the user authentication, session selection, and user consent.
The result is an access token, which the client should validate before including it in a Google API request. When the token expires, the application repeats the process.
Applications on limited-input devices
The Google OAuth 2.0 endpoint supports applications that run on limited-input devices such as game consoles, video cameras, and printers.
The authorization sequence begins with the application making a web service request to a Google URL for an authorization code. The response contains several parameters, including a URL and a code that the application shows to the user.
The user obtains the URL and code from the device, then switches to a separate device or computer with richer input capabilities. The user launches a browser, navigates to the specified URL, logs in, and enters the code.
Meanwhile, the application polls a Google URL at a specified interval. After the user approves access, the response from the Google server contains an access token and refresh token. The application should store the refresh token for future use and use the access token to access a Google API. Once the access token expires, the application uses the refresh token to obtain a new one.
The user logs in on a separate device that has a browser.
For details, see Using OAuth 2.0 for Devices.
Google APIs such as the Prediction API and Google Cloud Storage can act on behalf of your application without accessing user information. In these situations your application needs to prove its own identity to the API, but no user consent is necessary. Similarly, in enterprise scenarios, your application can request delegated access to some resources.
For these types of server-to-server interactions you need a service account, which is an account that belongs to your application instead of to an individual end-user. Your application calls Google APIs on behalf of the service account, and user consent is not required. (In non-service-account scenarios, your application calls Google APIs on behalf of end-users, and user consent is sometimes required.)
Note: These service-account scenarios require applications to create and cryptographically sign
JSON Web Tokens (JWTs). We strongly encourage you to use a library to perform these tasks. If you write this code without using a library that abstracts token creation and signing, you might make errors that would have a severe impact on the security of your application. For a list of libraries that support this scenario, see the service-account documentation.
A service account's credentials, which you obtain from the Google API Console, include a generated email address that is unique, a client ID, and at least one public/private key pair. You use the client ID and one private key to create a signed JWT and construct an access-token request in the appropriate format. Your application then sends the token request to the Google OAuth 2.0 Authorization Server, which returns an access token. The application uses the token to access a Google API. When the token expires, the application repeats the process.
Your server application uses a JWT to request a token from the Google Authorization Server,
then uses the token to call a Google API endpoint. No end-user is involved.
For details, see the service-account documentation.
Note: Although you can use service accounts in applications that run from a G Suite domain, service accounts are not members of your G Suite account and aren’t subject to domain policies set by G Suite administrators. For example, a policy set in the G Suite admin console to restrict the ability of G Suite end users to share documents outside of the domain would not apply to service accounts.
Token expiration
You must write your code to anticipate the possibility that a granted token might no longer work. A token might stop working for one of these reasons:
The user has revoked access.
The token has not been used for six months.
The user changed passwords and the token contains Gmail scopes.
The user account has exceeded a certain number of token requests.
There is currently a limit of 50 refresh tokens per user account per client. If the limit is reached, creating a new token automatically invalidates the oldest token without warning. This limit does not apply to service accounts.
There is also a larger limit on the total number of tokens a user account or service account can have across all clients. Most normal users won't exceed this limit but a developer's test account might.
If you need to authorize multiple programs, machines, or devices, one workaround is to limit the number of clients that you authorize per user account to 15 or 20. If you are a G Suite admin, you can create additional admin users and use them to authorize some of the clients.
Client libraries
The following client libraries integrate with popular frameworks, which makes implementing OAuth 2.0 simpler. More features will be added to the libraries over time.
Google API Client Library for Java
Google API Client Library for Python
Google API Client Library for Go
Google API Client Library for .NET
Google API Client Library for Ruby
Google API Client Library for PHP
Google API Client Library for JavaScript
GTMAppAuth - OAuth Client Library for Mac and iOS
最終更新：2017年03月26日 12:13
