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xmpp-cloud-auth

This authentication script for ejabberd and prosody allows to authenticate against a Nextcloud/Owncloud instance running OJSXC (>= 3.2.0).

Installation

Download external_cloud.py and put it to your desired location or clone this repository to simplify updates:

cd /opt
git clone https://github.com/jsxc/xmpp-cloud-auth

Make the script executable and give your ejabberd/prosody user sufficient rights:

chmod u+x xmpp-cloud-auth/external_cloud.py
chown USER:GROUP -R xmpp-cloud-auth

Install python and all desired libraries.

sudo apt-get install python python-pip
sudo -u USER -H pip install requests

Ejabberd

Adjust your configuration as described in the admin manual.

vim /etc/ejabberd/ejabberd.yml

auth_method: external
extauth_program: "/opt/xmpp-cloud-auth/external_cloud.py -t ejabberd -u APIURL -s APISECRET"

You will find the values for APIURL and APISECRET on your Nextcloud/Owncloud admin page.

⚠️ On Ubuntu ejabberd will come with an apparmor profile which will block the external authentication script. See also the related issue.

Prosody

Install mod_auth_external and add the following to your config:

authentication = "external"
external_auth_command = "/opt/ejabberd-cloud-auth/external_cloud.py -t prosody -u APIURL -s APISECRET -l /var/log/prosody"

You will find the values for APIURL and APISECRET on your Nextcloud/Owncloud admin page.

⚠️ The current module has some issue, see also #1 and #2.

Options

$ ./external_cloud.py --help
usage: external_cloud.py [-h] -t {prosody,ejabberd} -u URL -s SECRET [-l LOG]
                         [-d]

XMPP server authentication script

optional arguments:
  -h, --help            show this help message and exit
  -t {prosody,ejabberd}, --type {prosody,ejabberd}
                        XMPP server
  -u URL, --url URL     base URL
  -s SECRET, --secret SECRET
                        secure api token
  -l LOG, --log LOG     log directory (default: /var/log/ejabberd)
  -d, --debug           toggle debug mode

How does it work?

Your XMPP server sends the authentication data in a special format on the standard input to the authentication script. The script will first try to verify the given password as time-limited token and if this fails, it will send a HTTP request to your cloud installation to verify this data. To protect your Nextcloud/Owncloud against different attacks, every request has a signature similar to the github webhook signature.

Time-limited token

The time-limited token has the following structure:

# Definitions
version := 'protocol version'
id := 'key id'
expiry := 'end of lifetime as unix timestamp'
user := 'user identifier'
secret := 'shared secret'
name[x] := 'first x bit of name'
, := 'concatenation'

# Calculation
version = hexToBin(0x00)
id = sha256(secret)
challenge = version[8],id[16],expiry[32],user
mac = sha256_mac(challenge, secret)
token = version[8],mac[128],id[16],expiry[32]

# Improve readability
token = base64_encode(token)
token = replace('=', '', token)
token = replace('O', '-', token)
token = replace('I', '$', token)
token = replace('l', '%', token)

Request signature

Every request to the API URL needs a HTTP_X_JSXC_SIGNATURE header:

body := 'request body'
secret := 'shared secret'

MAC = sha1_hmac(body, secret)

HTTP_X_JSXC_SIGNATURE: sha1=MAC