Private channels¶
In channels chapter we mentioned private channels. This chapter has more information about private channel mechanism in Centrifugo.
All channels starting with $ considered private. In this case your backend should additionally provide token for every subscription request to such a channel. This way you can control subscription permissions and only allow certain users to subscribe to a channel.
The way how this token obtained varies depending on client implementation.
For example in Javascript client AJAX POST request automatically sent to /centrifuge/subscribe endpoint on every private channel subscription attempt. Other client libraries can provide a hook for your custom code that will obtain private channel subscription token from application backend.
Private channel subscription token is also JWT (like connection token described in authentication chapter). But it has different claims.
Note
Connection token and private channel subscription token are different entities. Though both are JWT, and you can generate them using any JWT library.
Note
Even when authorizing subscription to private channel with private subscription JWT you should set a proper connection JWT for a client as it provides user authentication details to Centrifugo.
Note
When you need to use namespace for private channel then the name of namespace should be written after $ symbol, i.e. if you have namespace name chat then private channel which belongs to that namespace must be written as sth like $chat:stream.
Supported JWT algorithms for private subscription tokens match algorithms to create connection JWT.
Claims¶
Private channel subscription token claims are: client, channel, info, b64info, exp and eto. What do they mean? Let's describe in detail.
client¶
Required. Client ID which wants to subscribe on a channel (string).
Note
Centrifugo server sets a unique client ID for each incoming connection. This client ID regenerated on every reconnect. You must use this client ID for private channel subscription token. If you are using centrifuge-js library then Client ID and Subscription Channels will be automaticaly added to POST request. In other cases refer to specific client documentation (in most cases you will have client ID in private subscription event context)
channel¶
Required. Channel that client tries to subscribe to (string).
info¶
Optional. Additional information for connection inside this channel (valid JSON).
b64info¶
Optional. Additional information for connection inside this channel in base64 format (string).
exp¶
Optional. This is standard JWT claim that allows to set private channel subscription token expiration time.
At moment if subscription token expires client connection will be closed and client will try to reconnect. In most cases you don't need this and should prefer using exp of connection token to deactivate connection. But if you need more granular per-channel control this may fit your needs.
Once exp set in token every subscription token must be periodically refreshed. Refer to specific client documentation in order to see how to refresh subscription tokens.
eto¶
Optional. An eto boolean flag can be used to indicate that Centrifugo must only check token expiration but not turn on Subscription expiration checks on server side. This allows to implement one-time subcription tokens.
Example¶
So to generate subscription token you can use something like this in Python (assuming client ID is XXX and private channel is $gossips):
import jwt
token = jwt.encode({"client": "XXX", "channel": "$gossips"}, "secret", algorithm="HS256").decode()
print(token)
Where "secret" is the token_hmac_secret_key from Centrifugo configuration (we use HMAC tokens in this example which relies on shared secret key, for RSA tokens you need to use private key known only by your backend).