Refactor docs (#21627)

This patch:
- Rename some files( `.md` to `.en-us.md`), fix missed translation copy
- Update link which shoud be refer to `../hacking-on-gitea/` instead of
`../make/` (outdated)
- Update `_redirects`:
  -  redirect `/{zh-cn|fr-fr}/make/` to `../hacking-on-gitea/`
  - redirect `/zh-cn/third-party-tools/` to `/zh-cn/integrations/`
- Delete duplicated/outdated files.
- Update menu `weight` of developers.zh-cn.md

Signed-off-by: Xinyu Zhou <i@sourcehut.net>

1 files changed, 104 insertions, 0 deletions

diff --git a/docs/content/doc/developers/oauth2-provider.en-us.md b/docs/content/doc/developers/oauth2-provider.en-us.md
new file mode 100644
index 0000000000..c6765f19e7
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+++ b/docs/content/doc/developers/oauth2-provider.en-us.md
@@ -0,0 +1,104 @@
+---
+date: "2019-04-19:44:00+01:00"
+title: "OAuth2 provider"
+slug: "oauth2-provider"
+weight: 41
+toc: false
+draft: false
+menu:
+  sidebar:
+    parent: "developers"
+    name: "OAuth2 Provider"
+    weight: 41
+    identifier: "oauth2-provider"
+---
+
+# OAuth2 provider
+
+**Table of Contents**
+
+{{< toc >}}
+
+Gitea supports acting as an OAuth2 provider to allow third party applications to access its resources with the user's consent. This feature is available since release 1.8.0.
+
+## Endpoints
+
+| Endpoint                 | URL                                 |
+| ------------------------ | ----------------------------------- |
+| OpenID Connect Discovery | `/.well-known/openid-configuration` |
+| Authorization Endpoint   | `/login/oauth/authorize`            |
+| Access Token Endpoint    | `/login/oauth/access_token`         |
+| OpenID Connect UserInfo  | `/login/oauth/userinfo`             |
+| JSON Web Key Set         | `/login/oauth/keys`                 |
+
+## Supported OAuth2 Grants
+
+At the moment Gitea only supports the [**Authorization Code Grant**](https://tools.ietf.org/html/rfc6749#section-1.3.1) standard with additional support of the following extensions:
+
+- [Proof Key for Code Exchange (PKCE)](https://tools.ietf.org/html/rfc7636)
+- [OpenID Connect (OIDC)](https://openid.net/specs/openid-connect-core-1_0.html#CodeFlowAuth)
+
+To use the Authorization Code Grant as a third party application it is required to register a new application via the "Settings" (`/user/settings/applications`) section of the settings.
+
+## Scopes
+
+Currently Gitea does not support scopes (see [#4300](https://github.com/go-gitea/gitea/issues/4300)) and all third party applications will be granted access to all resources of the user and their organizations.
+
+## Client types
+
+Gitea supports both confidential and public client types, [as defined by RFC 6749](https://datatracker.ietf.org/doc/html/rfc6749#section-2.1).
+
+For public clients, a redirect URI of a loopback IP address such as `http://127.0.0.1/` allows any port. Avoid using `localhost`, [as recommended by RFC 8252](https://datatracker.ietf.org/doc/html/rfc8252#section-8.3).
+
+## Example
+
+**Note:** This example does not use PKCE.
+
+1. Redirect to user to the authorization endpoint in order to get their consent for accessing the resources:
+
+   ```curl
+   https://[YOUR-GITEA-URL]/login/oauth/authorize?client_id=CLIENT_ID&redirect_uri=REDIRECT_URI& response_type=code&state=STATE
+   ```
+
+   The `CLIENT_ID` can be obtained by registering an application in the settings. The `STATE` is a random string that will be send back to your application after the user authorizes. The `state` parameter is optional but should be used to prevent CSRF attacks.
+
+   ![Authorization Page](/authorize.png)
+
+   The user will now be asked to authorize your application. If they authorize it, the user will be redirected to the `REDIRECT_URL`, for example:
+
+   ```curl
+   https://[REDIRECT_URI]?code=RETURNED_CODE&state=STATE
+   ```
+
+2. Using the provided `code` from the redirect, you can request a new application and refresh token. The access token endpoints accepts POST requests with `application/json` and `application/x-www-form-urlencoded` body, for example:
+
+   ```curl
+   POST https://[YOUR-GITEA-URL]/login/oauth/access_token
+   ```
+
+   ```json
+   {
+     "client_id": "YOUR_CLIENT_ID",
+     "client_secret": "YOUR_CLIENT_SECRET",
+     "code": "RETURNED_CODE",
+     "grant_type": "authorization_code",
+     "redirect_uri": "REDIRECT_URI"
+   }
+   ```
+
+   Response:
+
+   ```json
+   {
+     "access_token": "eyJhbGciOiJIUzUxMiIsInR5cCI6IkpXVCJ9.eyJnbnQiOjIsInR0IjowLCJleHAiOjE1NTUxNzk5MTIsImlhdCI6MTU1NTE3NjMxMn0.0-iFsAwBtxuckA0sNZ6QpBQmywVPz129u75vOM7wPJecw5wqGyBkmstfJHAjEOqrAf_V5Z-1QYeCh_Cz4RiKug",
+     "token_type": "bearer",
+     "expires_in": 3600,
+     "refresh_token": "eyJhbGciOiJIUzUxMiIsInR5cCI6IkpXVCJ9.eyJnbnQiOjIsInR0IjoxLCJjbnQiOjEsImV4cCI6MTU1NzgwNDMxMiwiaWF0IjoxNTU1MTc2MzEyfQ.S_HZQBy4q9r5SEzNGNIoFClT43HPNDbUdHH-GYNYYdkRfft6XptJBkUQscZsGxOW975Yk6RbgtGvq1nkEcklOw"
+   }
+   ```
+
+   The `CLIENT_SECRET` is the unique secret code generated for this application. Please note that the secret will only be visible after you created/registered the application with Gitea and cannot be recovered. If you lose the secret you must regenerate the secret via the application's settings.
+
+   The `REDIRECT_URI` in the `access_token` request must match the `REDIRECT_URI` in the `authorize` request.
+
+3. Use the `access_token` to make [API requests](https://docs.gitea.io/en-us/api-usage#oauth2) to access the user's resources.