# 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. 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()