synapse/docs/admin_api/register_api.md

Shared-Secret Registration

This API allows for the creation of users in an administrative and non-interactive way. This is generally used for bootstrapping a Synapse instance with administrator accounts.

To authenticate yourself to the server, you will need both the shared secret (registration_shared_secret in the homeserver configuration), and a one-time nonce. If the registration shared secret is not configured, this API is not enabled.

To fetch the nonce, you need to request one from the API:

> GET /_synapse/admin/v1/register

< {"nonce": "thisisanonce"}

Once you have the nonce, you can make a POST to the same URL with a JSON body containing the nonce, username, password, whether they are an admin (optional, False by default), and a HMAC digest of the content. Also you can set the displayname (optional, username by default).

As an example:

> POST /_synapse/admin/v1/register
> {
   "nonce": "thisisanonce",
   "username": "pepper_roni",
   "displayname": "Pepper Roni",
   "password": "pizza",
   "admin": true,
   "mac": "mac_digest_here"
  }

< {
   "access_token": "token_here",
   "user_id": "@pepper_roni:localhost",
   "home_server": "test",
   "device_id": "device_id_here"
  }

The MAC is the hex digest output of the HMAC-SHA1 algorithm, with the key being the shared secret and the content being the nonce, user, password, either the string "admin" or "notadmin", and optionally the user_type each separated by NULs.

Here is an easy way to generate the HMAC digest if you have Bash and OpenSSL:

# Update these values and then paste this code block into a bash terminal
nonce='thisisanonce'
username='pepper_roni'
password='pizza'
admin='admin'
secret='shared_secret'

printf '%s\0%s\0%s\0%s' "$nonce" "$username" "$password" "$admin" |
  openssl sha1 -hmac "$secret" |
  awk '{print $2}'

For an example of generation in Python:

import hmac, hashlib

def generate_mac(nonce, user, password, admin=False, user_type=None):

    mac = hmac.new(
      key=shared_secret,
      digestmod=hashlib.sha1,
    )

    mac.update(nonce.encode('utf8'))
    mac.update(b"\x00")
    mac.update(user.encode('utf8'))
    mac.update(b"\x00")
    mac.update(password.encode('utf8'))
    mac.update(b"\x00")
    mac.update(b"admin" if admin else b"notadmin")
    if user_type:
        mac.update(b"\x00")
        mac.update(user_type.encode('utf8'))

    return mac.hexdigest()