Use access tokens from the environment

Closes #4

main.go

@@ -34,10 +34,13 @@ var (
 
 	serviceName = app.Arg("serviceName", "Service name to ssh to").String()
 
-	accessToken = app.Flag("at", "Access Token").Short('a').Required().String()
-	issuerURI   = app.Flag("issuer", "Issuer URI of your access token").Short('i').Default("https://unity.helmholtz-data-federation.de/oauth2").String()
-	feudalURI   = app.Flag("uri", "Feudal URI").Short('u').Default("https://hdf-portal-dev.data.kit.edu").String()
-	pubKey      = app.Flag("pubkey", "SSH public key file path").Short('k').Required().String()
+	// access token, possibly from the environment
+	// Envar OIDC has precedence over OIDC_AT
+	accessToken = app.Flag("at", "Access Token").Short('a').Envar("OIDC_AT").Envar("OIDC").Required().String()
+
+	issuerURI = app.Flag("issuer", "Issuer URI of your access token").Short('i').Default("https://unity.helmholtz-data-federation.de/oauth2").String()
+	feudalURI = app.Flag("uri", "Feudal URI").Short('u').Default("https://hdf-portal-dev.data.kit.edu").String()
+	pubKey    = app.Flag("pubkey", "SSH public key file path").Short('k').Required().String()
 )
 
 func restCall(method string, path string, body io.Reader) (responseBytes []byte, err error) {