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+google-calendar-rsvp
+====================
+
+RSVP to a Google Calendar event invitation from the command line.
+
+In March 2021, [Google announced that RSVP hyperlinks in Google Calendar
+invitation emails would require authentication][sign-in to RSVP announcement].
+Previously, I had been using this script to accept calendar invitations in Mutt:
+
+``` shell
+#!/bin/sh
+
+# google-calendar-invite-accept.sh
+# Given a Google Calendar invite email on standard input, accept the invite.
+
+EX_DATAERR=65
+
+ampersand='%26'
+equal_sign='%3D'
+
+accept_invite='1'
+
+
+accept_url=$($HOME/.mutt/scripts/extract_url/extract_url.pl <&0 |
+	fgrep "${ampersand}rst${equal_sign}${accept_invite}${ampersand}" |
+	perl -MURI::Escape -e 'print uri_unescape(<STDIN>)')
+
+if [ -z "$accept_url" ]; then
+	echo >&2 'google-calendar-invite-accept.sh: error: no acceptance URL'
+	exit $EX_DATAERR
+fi
+
+curl -L "$accept_url" |
+	w3m -dump -T text/html
+```
+
+Since the authentication change, I was forced to open the acceptance link in a
+browser. This program enables you to RSVP to the invitation without leaving your
+email client.
+
+[sign-in to RSVP announcement]: https://workspaceupdates.googleblog.com/2021/03/sign-in-to-rsvp-via-hyperlinks-in.html
+
+
+## Usage
+
+	$ google-calendar-rsvp --yes 1g4j1h67ndq7kddrb2bptp2cua
+	$ google-calendar-rsvp --maybe \
+		1g4j1h67ndq7kddrb2bptp2cua \
+		MWc0ajFoNjduZHE3a2RkcmIyYnB0cDJjdWEgcm9yeS5tZXJjdXJ5QGV4YW1wbGUuY28K
+	$ google-calendar-rsvp --email --no < invitation.eml
+
+
+## Authentication
+In order to authenticate with Google and RSVP to calendar invitations:
+
+1. Create a new project on the [Google Developer Console]
+2. Add the Google Calendar API to the project
+3. Create an OAuth 2.0 client ID
+4. Download the OAuth JSON client secret file to
+   `$XDG_DATA_HOME/google-calendar-rsvp/oauth-secret.json`
+
+
+[Google Developer Console]: https://console.developers.google.com/
+
+
+## Install
+On Mac OS X, Google Calendar RSVP can be installed with Homebrew:
+
+	$ brew install teddywing/formulae/google-calendar-rsvp
+
+To compile from source or install on other platforms:
+
+	$ cargo install --git https://github.com/teddywing/google-calendar-rsvp.git
+
+
+## Uninstall
+
+	$ cargo uninstall google-calendar-rsvp
+
+
+## License
+Copyright © 2021 Teddy Wing. Licensed under the GNU GPLv3+ (see the included
+COPYING file).