Assert TLS configuration when booting MongoosePush

[leszke]

The purpose of this PR is to prevent MPush from start when APNS required ciphers (ECDHE-RSA-AES128-GCM-SHA256 and ECDHE-RSA-AES256-GCM-SHA384) are not available in runtime. In this scenario user receives error message, briefly explaining what's going on.
Use case examples:

$ _build/prod/rel/mongoose_push/bin/mongoose_push foreground
when=2020-07-17T17:36:03.985 severity=info what=init text="Starting PoolsWarden" at=Elixir.Sparrow.PoolsWarden.init/1:95 pid=#PID<0.1826.0> result=success worker=pools_warden file=lib/sparrow/pools_warden.ex application=sparrow
{"application":"mongoose_push","at":"Elixir.MongoosePush.Application.check_apns_ciphers/0:234","file":"lib/mongoose_push/application.ex","pid":"#PID<0.1880.0>","reason":"no_apns_ciphers","severity":"error","status":"error","text":"APNS required ciphers missing","what":"tls_configuration","when":"2020-07-17T17:36:04.040"}
{"at":"application_controller.info_exited/3:1943","file":"application_controller.erl","pid":"#PID<0.1660.0>","severity":"info","text":"Application mongoose_push exited: MongoosePush.Application.start(:normal, []) returned an error: :no_apns_ciphers","what":"","when":"2020-07-17T17:36:04.040"}
=SUPERVISOR REPORT==== 17-Jul-2020::17:36:04.066666 ===
    supervisor: {local,gr_counter_sup}
    errorContext: child_terminated
    reason: killed
    offender: [{pid,<0.1742.0>},
               {id,gr_lager_default_tracer_counters},
               {mfargs,{gr_counter,start_link,
                                   [gr_lager_default_tracer_counters]}},
               {restart_type,transient},
               {shutdown,brutal_kill},
               {child_type,worker}]

=SUPERVISOR REPORT==== 17-Jul-2020::17:36:04.066749 ===
    supervisor: {local,gr_param_sup}
    errorContext: child_terminated
    reason: killed
    offender: [{pid,<0.1741.0>},
               {id,gr_lager_default_tracer_params},
               {mfargs,{gr_param,start_link,[gr_lager_default_tracer_params]}},
               {restart_type,transient},
               {shutdown,brutal_kill},
               {child_type,worker}]

{"Kernel pid terminated",application_controller,"{application_start_failure,mongoose_push,{no_apns_ciphers,{'Elixir.MongoosePush.Application',start,[normal,[]]}}}"}
Kernel pid terminated (application_controller) ({application_start_failure,mongoose_push,{no_apns_ciphers,{'Elixir.MongoosePush.Application',start,[normal,[]]}}})

Crash dump is being written to: erl_crash.dump...done

$ iex -S mix
Erlang/OTP 23 [erts-11.0] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [hipe]

Compiling 60 files (.ex)
Compiling 1 file (.erl)
when=2020-07-17T17:40:32.855 severity=info what=init text="Starting PoolsWarden" at=Elixir.Sparrow.PoolsWarden.init/1:95 pid=#PID<0.809.0> result=success worker=pools_warden file=lib/sparrow/pools_warden.ex application=sparrow
when=2020-07-17T17:40:32.955 severity=error what=tls_configuration text="APNS required ciphers missing" at=Elixir.MongoosePush.Application.check_apns_ciphers/0:234 pid=#PID<0.841.0> reason=no_apns_ciphers status=error file=lib/mongoose_push/application.ex application=mongoose_push
** (Mix) Could not start application mongoose_push: MongoosePush.Application.start(:normal, []) returned an error: :no_apns_ciphers

[michalwski]

Thanks for adding the cipher suites check at application startup. This clearly defines why the app couldn't start. I had just one cosmetic suggestion, just let me know if you want to change the code or not.
The PR is ready to be merged with or without addressing my comment.

[michalwski]

Just a cosmetic thing. It looks like to me, that Enum.any? could be used instead of Enum.fiter, thanks to that we'll have the answer immediately, without the need to calculate the length of the new list.

[leszke]

Corrected. But in exchange we've lost the underscore and have to match to :aead directly.

[michalwski]

I think the previous fun used with filter would work as well. Anyway, thanks for applying my suggestion.

[janciesla8818]

Looks good. Thanks for adding this.