diff --git a/README.md b/README.md
index 291d187..c05f690 100644
--- a/README.md
+++ b/README.md
@@ -210,7 +210,16 @@ Multiple upstreams can either be configured by supplying a comma separated list
 
 ### Environment variables
 
-The environment variables `OAUTH2_PROXY_CLIENT_ID`, `OAUTH2_PROXY_CLIENT_SECRET`, `OAUTH2_PROXY_COOKIE_SECRET`, `OAUTH2_PROXY_COOKIE_DOMAIN` and `OAUTH2_PROXY_COOKIE_EXPIRE` can be used in place of the corresponding command-line arguments.
+The following environment variables can be used in place of the corresponding command-line arguments:
+
+- `OAUTH2_PROXY_CLIENT_ID`
+- `OAUTH2_PROXY_CLIENT_SECRET`
+- `OAUTH2_PROXY_COOKIE_NAME`
+- `OAUTH2_PROXY_COOKIE_SECRET`
+- `OAUTH2_PROXY_COOKIE_DOMAIN`
+- `OAUTH2_PROXY_COOKIE_EXPIRE`
+- `OAUTH2_PROXY_COOKIE_REFRESH`
+- `OAUTH2_PROXY_SIGNATURE_KEY`
 
 ## SSL Configuration
 
diff --git a/options.go b/options.go
index 5d4c86f..37e66b4 100644
--- a/options.go
+++ b/options.go
@@ -64,7 +64,7 @@ type Options struct {
 
 	RequestLogging bool `flag:"request-logging" cfg:"request_logging"`
 
-	SignatureKey string `flag:"signature-key" cfg:"signature_key"`
+	SignatureKey string `flag:"signature-key" cfg:"signature_key" env:"OAUTH2_PROXY_SIGNATURE_KEY"`
 
 	// internal values that are set after config validation
 	redirectURL   *url.URL