forward_to_gmail reads an email from stdin and inserts it into a
user's Gmail account using the Gmail API with narrowly-scoped OAuth2
credentials.  You can feed incoming emails to forward_to_gmail using
procmail or .forward to "forward" the messages to Gmail without using
SMTP.  (SMTP mail forwarding is broken because it causes backscatter
and negatively affects the reputation of the forwarding IP address.)


ENVIRONMENT VARIABLES

The following environment variables must be set to use forward_to_gmail:

	$GMAIL_CLIENT_ID	Your OAuth2 client ID
	$GMAIL_CLIENT_SECRET	Your OAuth2 client secret
	$GMAIL_TOKEN		Your OAuth2 token

To obtain a client ID and client secret, follow the steps under "Obtaining
Client Credentials" below.  These credentials only need to be obtained
once and can be shared among all users of an organization.

To obtain a token, follow the steps under "Obtaining a Token" below.
This token is tied to a particular Gmail account and only needs to
be obtained once as long as the user does not revoke it.



OBTAINING CLIENT CREDENTIALS

1. Go to:

	https://console.developers.google.com/start/api?id=gmail&credential=client_key

2. Create a new project or select an existing project and click "Continue"

3. On the "Add credentials to your project" page:

	1. Select:
		Which API are you using? => "Gmail API"
		Where will you be calling the API from? => "Other UI (e.g. Windows, CLI tool)"
		What data will you be accessing? => "User data"

	2. Click "What Credentials Do I Need?"

	3. Enter a client ID name of your choosing and click "Create client ID"

	4. Customize the consent screen as you like and click "Continue"

	5. Click "Done"

4. Click the name of your client ID.  Make note of your client ID and
client secret, which should be assigned to the $GMAIL_CLIENT_ID and
$GMAIL_CLIENT_SECRET variables, respectively.


OBTAINING A TOKEN

First you must obtain client credentials and set the $GMAIL_CLIENT_ID
and $GMAIL_CLIENT_SECRET environment variables.

1. Run `forward_to_gmail -get_url` and go to the URL that it outputs.

2. Log in with your Google account and authorize forward_to_gmail.

3. Run `forward_to_gmail -get_token CODE`, replacing CODE with the code
provided by Gmail.

4. Make note of the token output by `forward_to_gmail`.  It should be
assigned to the $GMAIL_TOKEN environment variable.