OAuth(开放授权)是访问授权/授权协议的开放标准。它是互联网用户授权网站或应用程序访问他们在其他网站上的信息而不提供密码的一种方式。它不处理身份验证。

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OAuth 2.0是一种协议，允许用户将其在一个站点上的资源的有限访问权限授予另一个站点，而无需暴露他们的凭据。

Analogy 1: Many luxury cars today come with a valet key. It is a special key you give the parking attendant and unlike your regular key, will not allow the car to drive more than a mile or two. Some valet keys will not open the trunk, while others will block access to your onboard cell phone address book. Regardless of what restrictions the valet key imposes, the idea is very clever. You give someone limited access to your car with a special key, while using your regular key to unlock everything. src from auth0 Analogy 2: Assume, we want to fill an application form for a bank account. Here Oauth works as, instead of filling the form by applicant, bank can fill the form using Adhaar or passport. Here the following three entities are involved: Applicant i.e. Owner Bank Account is OAuth Client, they need information Adhaar/Passport ID is OAuth Provider

OAuth是什么?

OAuth只是一个安全的授权协议，用于处理第三方应用程序的授权，以便在不暴露用户密码的情况下访问用户数据。(例如，在许多网站上登录Facebook, gPlus, Twitter)都在此协议下工作。

各方

当你了解有关各方时，议定书就变得更容易了。基本上，涉及到三个方面:OAuth提供者、OAuth客户端和所有者。

OAuth客户端(想要访问您的凭据的应用程序) OAuth提供者(例如;Facebook, Twitter等) 所有者(拥有Facebook、Twitter等账户的人)

工作原理

我假设了一个场景，一个网站(Stack Overflow)需要添加一个登录与Facebook功能。因此，Facebook是OAuth提供者，Stack Overflow是OAuth客户端。

This step is done by the app's developer. At the very beginning, Facebook (OAuth Provider) has no idea about the Stack Overflow (OAuth Client) because there is no link between them. So the very first step is to register Stack Overflow with Facebook developers site. This is done manually where developers need to give the app's information to Facebook like the app's name, website, logo, redirectUrl (important one). Then Stack Overflow is successfully registered, has got client Id, client secret, etc from Facebook, and is up and running with OAuth.

现在当Stack Overflow的用户点击登录Facebook按钮。Stack Overflow请求Facebook使用ClientId (Facebook使用它来识别客户端)和redirectUrl(成功后Facebook将返回此URL)。因此，用户被重定向到Facebook登录页面。这是最好的部分，用户(所有者)不会把他们的Facebook凭证给Stack Overflow。

After Owner allows Stack Overflow to access the information. Then Facebook redirects back to Stack Overflow, along with authcode using the redirectUrl provided at step 2. Then Stack Overflow contacts Facebook along with the obtained authcode to make sure everything is okay. Only then Facebook will give access token to Stack Overflow. Then access token is used by Stack Overflow to retrieve the owner's information without using a password. This is the whole motive of OAuth, where actual credentials are never exposed to third-party applications.

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OAuth是一种开放的授权标准，通常用于互联网用户使用微软、谷歌、Facebook或Twitter账户登录第三方网站而不暴露密码。

授权:OAuth顾名思义只是一种授权标准。

用于登录第三方网站:使用OAuth，您可以使用您的谷歌，Facebook, Twitter或微软帐户登录第三方网站，而无需提供密码。

记住密码:使用OAuth，你可以避免在你在互联网上使用的每个web应用程序上创建帐户和记住密码。

Access token: OAuth is based on an access token concept. When a person authenticate hinself using his Google account, to a third party web application. Google authorization server issues an access token for that web application the person is using. Thus, the web application can use that access token to access his data hosted in the resource server. In the case of Google, your Gmail inbox, contacts, photos etc. are the resources. So, any third party application can access those resources, for an example view his Gmail inbox using OAuth. Hence, OAuth is a simple way to publish and interact with protected resource data. It’s also a safer and more secure way for people to give you access to their resource data.

OAuth2和HTTPS:由于机密数据(例如客户端凭证)，OAuth2使用HTTPS在客户端和授权服务器之间进行通信。在两个应用程序之间传递。

OAuth是Resource Owner(facebook，谷歌，tweeter, microsoft live等)使用的协议，用于提供所需的信息，或为第三方系统(例如您的站点)提供写入成功的许可。最有可能的是，如果没有OAuth协议，第三方系统应该可以使用凭据，这将是这些系统之间不合适的通信方式。

Simply put OAuth is a way for applications to gain credentials to your information without directly getting your user login information to some website. For example if you write an application on your own website and want it to use data from a user's facebook account, you can use OAuth to get a token via a callback url and then use that token to make calls to the facebook API to get their use data until the token expires. Websites rely on it because it allows programmers to access their data without the user having to directly disclose their information and spread their credentials around online but still provide a level of protection to the data. Will it become the de facto method of authorization? Perhaps, it's been gaining a lot of support recently from Twitter, Facebook, and the likes where other programmers want to build applications around user data.