Cent

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Improvements:

* Support passing `api_key` over URL param, see [317](https://github.com/centrifugal/centrifugo/issues/317) for reasoning behind this feature

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This is a quick fix release. Fixes an error on start when `namespaces` not set in configuration file,the bug was introduced in v2.2.5, see [319](https://github.com/centrifugal/centrifugo/issues/319) for details.

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Centrifugo now uses `https://cdn.jsdelivr.net/npm/sockjs-client1/dist/sockjs.min.js` as default SockJS url. This allows Centrifugo to always be in sync with recent v1 SockJS client. This is important to note because SockJS requires client versions to exactly match on server and client sides when using transports involving iframe. Don't forget that Centrifugo has `sockjs_url` option to set custom SockJS URL to use on server side.

Improvements:

* support setting all configuration options over environment variables in format `CENTRIFUGO_<OPTION_NAME>`. This was available before but starting from this release we will support setting **all** options over env
* show HTTP status code in logs when debug log level on
* option to customize HTTP handler endpoints, see [docs](https://centrifugal.github.io/centrifugo/server/configuration/#customize-handler-endpoints)
* possibility to provide custom key and cert files for GRPC API server TLS, see `centrifugo -h` for a bunch of new options

Fixes:

* Fix setting `presence_disable_for_client` and `history_disable_for_client` on config top level
* Fix Let's Encrypt integration by updating to ACMEv2 / RFC 8555 compilant acme library, see [311](https://github.com/centrifugal/centrifugo/issues/311)

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No backwards incompatible changes here.

Improvements:

* Improve web interface: show total client information (sum of all client connections on all running nodes)

Fixes:

* Fixes SockJS WebSocket 403 response for cross domain requests: this is a regression in v2.2.3

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No backwards incompatible changes here.

Improvements:

* New chapter in docs: [Benchmarking server](https://centrifugal.github.io/centrifugo/misc/benchmark/). This chapter contains information about test stand inside Kubernetes with million WebSocket connections to a server based on Centrifuge library (the core of Centrifugo). It gives some numbers and insights about hardware requirements and scalability of Centrifugo
* New channel and channel namespace options: `presence_disable_for_client` and `history_disable_for_client`. `presence_disable_for_client` allows to make presence available only for server side API. `history_disable_for_client` allows to make history available only for server side API. Previously when enabled presence and history were available for both client and server APIs. Now you can disable for client side. History recovery mechanism if enabled will continue to work for clients anyway even if `history_disable_for_client` is on
* Wait for close handshake completion before terminating WebSocket connection from server side. This allows to gracefully shutdown WebSocket sessions

Fixes:

* Fix crash due to race condition, race reproduced when history recover option was on. See [commit](https://github.com/centrifugal/centrifuge/pull/73/files) with fix details
* Fix lack of `client_anonymous` option. See [304](https://github.com/centrifugal/centrifugo/issues/304)

This release based on Go 1.13.x

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No backwards incompatible changes here.

Improvements:

* Support for `tls-alpn-01` ACME challenge, see [283](https://github.com/centrifugal/centrifugo/issues/283)

Fixes:

* fix running HTTP server several times when http-01 ACME challenge used, see [288](https://github.com/centrifugal/centrifugo/issues/288)