Document request-logging-format option

README.md

@@ -194,6 +194,7 @@ Usage of oauth2_proxy:
   -redeem-url string: Token redemption endpoint
   -redirect-url string: the OAuth Redirect URL. ie: "https://internalapp.yourcompany.com/oauth2/callback"
   -request-logging: Log requests to stdout (default true)
+  -request-logging-format: Template for request log lines (see "Logging Format" paragraph below)
   -resource string: The resource that is protected (Azure AD only)
   -scope string: OAuth scope specification
   -set-xauthrequest: set X-Auth-Request-User and X-Auth-Request-Email response headers (useful in Nginx auth_request mode)
@@ -331,12 +332,21 @@ following:
 
 ## Logging Format
 
-OAuth2 Proxy logs requests to stdout in a format similar to Apache Combined Log.
+By default, OAuth2 Proxy logs requests to stdout in a format similar to Apache Combined Log.
 
 ```
 <REMOTE_ADDRESS> - <user@domain.com> [19/Mar/2015:17:20:19 -0400] <HOST_HEADER> GET <UPSTREAM_HOST> "/path/" HTTP/1.1 "<USER_AGENT>" <RESPONSE_CODE> <RESPONSE_BYTES> <REQUEST_DURATION>
 ```
 
+If you require a different format than that, you can configure it with the `-request-logging-format` flag.
+The default format is configured as follows:
+
+```
+{{.Client}} - {{.Username}} [{{.Timestamp}}] {{.Host}} {{.RequestMethod}} {{.Upstream}} {{.RequestURI}} {{.Protocol}} {{.UserAgent}} {{.StatusCode}} {{.ResponseSize}} {{.RequestDuration}}
+```
+
+[See `logMessageData` in `logging_handler.go`](./logging_handler.go) for all available variables.
+
 ## Adding a new Provider
 
 Follow the examples in the [`providers` package](providers/) to define a new