pizauth: an OAuth2 token requester daemon

pizauth is a simple program for requesting, showing, and refreshing OAuth2 access tokens. pizauth is formed of two components: a persistent server which interacts with the user to request tokens, and refreshes them as necessary; and a command-line interface which can be used by programs such as fdm and msmtp to authenticate with OAuth2.

Quick setup

pizauth’s configuration file is ~/.config/pizauth.conf. You need to specify at least one account, which tells pizauth how to authenticate against a particular OAuth2 setup. Most users will also want to receive asynchronous notifications of authorisation requests and errors, which requires setting auth_notify_cmd and error_notify_cmd. See the bundled example configuration for more details.

Account setup

At a minimum you need to find out from your provider:

• The authorisation URI.
• The token URI.
• Your "Client ID" (and in many cases also your "Client secret"), which identify your software.
• (In some cases) The scope(s) which your OAuth2 access token will give you access to. For pizauth to be able to refresh tokens, you may need to add an explicit offline_access scope.
• (In some cases) The redirect URI (you must copy this exactly, including trailing slash / characters). The default value of http://localhost/ suffices in most instances.

Some providers allow you to create Client IDs and Client Secrets at will (e.g. Google). Some providers sometimes allow you to create Client IDs and Client Secrets (e.g. Microsoft Azure but allow organisations to turn off this functionality.

For example, to create an account called officesmtp which obtains OAuth2 tokens which allow you to read email via IMAP and send email via Office365’s servers:

account "officesmtp" {
auth_uri = "https://login.microsoftonline.com/common/oauth2/v2.0/authorize";
token_uri = "https://login.microsoftonline.com/common/oauth2/v2.0/token";
client_id = "..."; // Fill in with your Client ID
client_secret = "..."; // Fill in with your Client secret
scopes = [
"https://outlook.office365.com/IMAP.AccessAsUser.All",
"https://outlook.office365.com/SMTP.Send",
"offline_access"
];
// You don't have to specify login_hint, but it does make authentication a
// little easier.
auth_uri_fields = { "login_hint": "email@example.com" };
}

Notifications

As standard, pizauth displays authorisation URLs and errors on stderr. If you want to use pizauth in the background, it is easy to miss such output. Fortunately, pizauth can run arbitrary commands to alert you that you need to authorise a new token, in essence giving you the ability to asynchronously display notifications. There are two main settings:

• auth_notify_cmd notifies users that an account needs authenticating. The command is run with two environment variables set:

• PIZAUTH_ACCOUNT is set to the account name to be authorised.

• PIZAUTH_URL is set to the authorisation URL.

• error_notify_cmd notifies users of errors. The command is run with two environment variables set:

• PIZAUTH_ACCOUNT is set to the account name to be authorised.

• PIZAUTH_MSG is set to the error message.

For example to use pizauth with notify-send:

auth_notify_cmd = "if [[ \"$(notify-send -A \"Open $PIZAUTH_ACCOUNT\" -t 30000 'pizauth authorisation')\" == \"0\" ]]; then open \"$PIZAUTH_URL\"; fi";
error_notify_cmd = "notify-send -t 90000 \"pizauth error for $PIZAUTH_ACCOUNT\" \"$PIZAUTH_MSG\"";

In this example, notify-send is used to open a notification with a "Open <account>" button; if that button is clicked, then the authorisation URL is opened in the user’s default web browser.

Running pizauth

You need to start the pizauth server (alternatively, start pizauth.service, see systemd-unit):

$ pizauth server

and configure software to request OAuth2 tokens with pizauth show officesmtp. The first time that pizauth show officesmtp is executed, it will print an error to stderr that includes an authorisation URL (and, if auth_notify_cmd is set, it will also execute that command):

$ pizauth show officesmtp
ERROR - Token unavailable until authorised with URL https://login.microsoftonline.com/common/oauth2/v2.0/authorize?access_type=offline&code_challenge=xpVa0mDzvR1Ozw5_cWN43DsO-k5_blQNHIzynyPfD3c&code_challenge_method=S256&scope=https%3A%2F%2Foutlook.office365.com%2FIMAP.AccessAsUser.All+https%3A%2F%2Foutlook.office365.com%2FSMTP.Send+offline_access&client_id=<your Client ID>&redirect_uri=http%3A%2F%2Flocalhost%3A14204%2F&response_type=code&state=%25E6%25A0%25EF%2503h6%25BCK&client_secret=<your Client Secret>&login_hint=email@example.com

The user then needs to open that URL in the browser of their choice and complete authentication. Once complete, pizauth will be notified, and shortly afterwards pizauth show officesmtp will start showing a token on stdout:

$ pizauth show officesmtp
DIASSPt7jlcBPTWUUCtXMWtj9TlPC6U3P3aV6C9NYrQyrhZ9L2LhyJKgl5MP7YV4

Note that:

1. pizauth show does not block: if a token is not available it will fail; once a token is available it will succeed.
2. pizauth show can print OAuth2 tokens which are no longer valid. By default, pizauth will continually refresh your token, but it may eventually become invalid. There will be a delay between the token becoming invalid and pizauth realising that has happened and notifying you to request a new token.

Command-line interface

pizauth’s usage is:

pizauth dump
pizauth refresh [-u] <account>
pizauth reload
pizauth restore
pizauth server [-c <config-path>] [-d]
pizauth show [-u] <account>
pizauth shutdown

Where:

• pizauth refresh tries to obtain a new access token for an account. If an access token already exists, a refresh is tried; if an access token doesn’t exist, a new request is made.
• pizauth reload causes the server to reload its configuration (this is a safe equivalent of the traditional SIGHUP mechanism).
• pizauth server starts a new instance of the server.
• pizauth show displays an access token, if one exists, for account. If an access token does not exist, a new request is initiated.
• pizauth shutdown asks the server to shut itself down.

pizauth dump and pizauth restore are explained in the Persistence section below.

Example integrations

Once you have set up pizauth, you will then need to set up the software which needs access tokens. This section contains example configuration snippets to help you get up and running.

In these examples, text in chevrons (like <this>) needs to be edited to match your individual setup. The examples assume that pizauth is in your $PATH: if it is not, you will need to substitute an absolute path to pizauth in these snippets.

msmtp

In your configuration file (typically ~/.config/msmtp/config):

account <account-name>
auth xoauth2
host <smtp-server>
protocol smtp
from <email-address>
user <username>
passwordeval pizauth show <pizauth-account-name>

mbsync

Ensure you have the xoauth2 plugin for cyrus-sasl installed, and then use something like this for the IMAP account in ~/.mbsyncrc:

IMAPAccount <account-name>
Host <imap-server>
User <username>
PassCmd "pizauth show <pizauth-account-name>"
AuthMechs XOAUTH2

Example account settings

Each provider you wish to authenticate with will have its own settings it requires of you. These can be difficult to find, so examples are provided in this section. Caveat emptor: these settings will not work in all situations, and providers have historically required users to intermittently change their settings.

Microsoft / Exchange

You may need to create your own client ID and secret by registering with Microsoft’s identity platform.

account "<your-account-name>" {
auth_uri = "https://login.microsoftonline.com/common/oauth2/v2.0/authorize";
auth_uri_fields = { "login_hint": "<your-email-address>" };
token_uri = "https://login.microsoftonline.com/common/oauth2/v2.0/token";
client_id = "<your-client-id>";
client_secret = "<your-client-secret>";
scopes = [
"https://outlook.office365.com/IMAP.AccessAsUser.All",
"https://outlook.office365.com/POP.AccessAsUser.All",
"https://outlook.office365.com/SMTP.Send",
"offline_access"
];
}

Gmail

You may need to create your own client ID and secret via the credentials tab of the Google Cloud Console.

account "<your-account-name>" {
auth_uri = "https://accounts.google.com/o/oauth2/auth";
auth_uri_fields = {"login_hint": "<your-email-address>"};
token_uri = "https://oauth2.googleapis.com/token";
client_id = "<your-client-id>";
client_secret = "<your-client-secret>";
scopes = ["https://mail.google.com/"];
}

Miele

You may need to create your own client ID and secret via the get involved tab of the Miele Developer site.

No scopes are needed.

account "<your-account-name>" {
auth_uri = "https://api.mcs3.miele.com/thirdparty/login/";
token_uri = "https://api.mcs3.miele.com/thirdparty/token/";
client_id = "<your-client-id>";
client_secret = "<your-client-secret>";
}

pizauth on a remote machine

You can run pizauth on a remote machine and have your local machine authenticate that remote existence with ssh -L. pizauth contains a small HTTP server used to receive authentication requests. By default the HTTP server listens on a random port, but it is easiest in this scenario to fix a port with the global http_listen option:

http_listen = "127.0.0.1:<port-number>";
account "..." { ... }

Then on your local machine (using the same <port-number> as above run ssh:

ssh -L 127.0.0.1:<port-number>:127.0.0.1:<port-number> <remote>

Then on the remote machine start pizauth server and then pizauth show <account-name>. Copy the authentication URL into a browser on your local machine and continue as normal. When you see the "pizauth processing authentication: you can safely close this page." message you can close the ssh tunnel. If the account later needs reauthenticating (e.g. because the refresh token has become invalid), simply reopen the ssh tunnel, reauthenticate, and close the ssh tunnel.

Persistence

By design, pizauth stores tokens state only in memory, and never to disk: users never have to worry that unencrypted secrets may be accessible on disk. However, if you use pizauth on a machine where pizauth is regularly restarted (e.g. because the machine is regularly rebooted), reauthenticating each time can be frustrating.

pizauth dump (which writes pizauth’s internal token state to stdout) and pizauth restore (which restores previously dumped token state read from stdin) allow you to persist state, but since they contain secrets they inevitably increase your security responsibilities. Although the output from pizauth dump may look like it is encrypted, it is trivial for an attacker to recover secrets from it: it is strongly recommended that you immediately encrypt the output from pizauth dump to avoid possible security issues.

The most common way to call pizauth dump is via the token_event_cmd configuration setting. token_event_cmd is called each time an account’s tokens change state (e.g. new tokens, refreshed tokens, etc). You can use this to run an arbitrary shell command such as pizauth dump:

token_event_cmd = "pizauth dump | age --encrypt --output pizauth.age -R age_public_key";

In this example, output from pizauth dump is immediately encrypted using age. In your machine’s startup process you can then call pizauth restore to restore the most recent dump e.g.:

age --decrypt -i age_private_key -o - pizauth.age | pizauth restore

Note that pizauth restore does not change the running pizauth’s configuration. Any changes in security relevant configuration between the dumping and restoring pizauth instances cause those parts of the dump to be silently ignored.

Alternatives

pizauth will not be perfect for everyone. You may also wish to consider these programs as alternatives:

• Email OAuth 2.0 Proxy
• mailctl
• mutt_oauth2.py
• oauth-helper-office-365