add docs for oauth connector

Signed-off-by: Rui Yang <ruiya@vmware.com>

README.md

@@ -80,6 +80,7 @@ Dex implements the following connectors:
 | [Atlassian Crowd](https://dexidp.io/docs/connectors/atlassiancrowd/) | yes | yes | yes * | beta | preferred_username claim must be configured through config |
 | [Gitea](https://dexidp.io/docs/connectors/gitea/) | yes | no | yes | alpha | |
 | [OpenStack Keystone](https://dexidp.io/docs/connectors/keystone/) | yes | yes | no | alpha | |
+| [Generic OAuth 2.0](https://dexidp.io/docs/connectors/oauth/) | no | yes | yes | beta |
 
 Stable, beta, and alpha are defined as:
 

docs/connectors/oauth.md

@@ -0,0 +1,49 @@
+# Authentication using Generic OAuth 2.0 provider
+
+## Overview
+
+Dex users can make use of this connector to work with standards-compliant [OAuth 2.0](https://oauth.net/2/) authorization provider, in case of that authorization provider is not in the Dex connectors list.
+
+## Configuration
+
+The following is an example of a configuration for using OAuth connector with Reddit.
+
+```yaml
+connectors:
+- type: oauth
+  # ID of OAuth 2.0 provider
+  id: reddit 
+  # Name of OAuth 2.0 provider
+  name: reddit
+  config:
+    # Connector config values starting with a "$" will read from the environment.
+    clientID: $REDDIT_CLIENT_ID
+    clientSecret: $REDDIT_CLIENT_SECRET
+    redirectURI: http://127.0.0.1:5556/callback
+
+    tokenURL: https://www.reddit.com/api/v1/access_token
+    authorizationURL: https://www.reddit.com/api/v1/authorize
+    userInfoURL: https: https://www.reddit.com/api/v1/me
+ 
+    # Optional: Specify whether to communicate to Auth provider without validating SSL certificates
+    # insecureSkipVerify: false
+
+    # Optional: The location of file containing SSL certificates to commmunicate to Auth provider 
+    # rootCAs: /etc/ssl/reddit.pem
+
+    # Optional: List of scopes to request Auth provider for access user account
+    # scopes:
+    #  - identity
+
+    # Optional: Configurable keys for user id field look up
+    # Default: groups
+    # groupsKey:
+
+    # Optional: Configurable keys for name field look up
+    # Default: user_id
+    # userIDKey:
+
+    # Optional: Configurable keys for username field look up
+    # Default: user_name
+    # userNameKey:
+```