Support newline-separated inputs for delegates and access_token_scopes (

#381)

Fixes #380

README.md

@@ -165,6 +165,8 @@ default, this action does not generate any tokens.
  https://www.googleapis.com/auth/cloud-platform
  ```
 
+ This can be specified as a comma-separated or newline-separated list.
+
 - `access_token_subject`: (Optional) Email address of a user to impersonate
  for [Domain-Wide Delegation][dwd]. Access tokens created for Domain-Wide
  Delegation cannot have a lifetime beyond 1 hour, even if the
@@ -277,7 +279,8 @@ regardless of the authentication mechanism.
 
 - `delegates`: (Optional) List of additional service account emails or unique
  identities to use for impersonation in the chain. By default there are no
- delegates.
+ delegates. This can be specified as a comma-separated or newline-separated
+ list.
 
 - `universe`: (Optional) The Google Cloud universe to use for constructing API
  endpoints. The default universe is "googleapis.com", which corresponds to