TLS :server: In state :certify received CLIENT ALERT: Fatal - Certificate Unknown

I’m trying to set up a self-signed certificate for a Phoenix app, but I’m getting log messages about “TLS :server: In state :certify received CLIENT ALERT: Fatal - Certificate Unknown”. I know others have posted about this, but I couldn’t seem to make things work following those posts.

I added a custom domain in /etc/hosts,

127.0.0.1       my-app.local

and then I created the self-signed certs: mix phx.gen.cert my-app my-app.local

Then I arranged my runtime.exs config to something like this:

config :my_app, MyAppWeb.Endpoint,
  url: [host: env!("PHX_HOST", :string)],
  https:[
      port: env!("PHX_PORT", :integer),
      cipher_suite: :strong,
      otp_app: :my_app,
      keyfile: env!("PHX_SSL_KEY_PATH", :string),
      certfile: env!("PHX_SSL_CERT_PATH", :string)
  ],
  force_ssl: [rewrite_on: [:x_forwarded_proto], host: nil],
  secret_key_base: env!("PHX_SECRET_KEY_BASE", :string)

I’m using dotenvy for the config values, but the above should be readable… host name is my-app.local, port is 4000, etc… but when I run mix phx.server, I get the dreaded CLIENT ALERT error:

17:26:05.108 module=ssl_alert function=decode/3 [notice] TLS :server: In state :certify received CLIENT ALERT: Fatal - Certificate Unknown

I tried following a similar post TLS error in dev (with self-signed certificates) and its link to APIacAuthMTLS — apiac_auth_mtls v1.0.0 but I wasn’t clear on how to integrate that with the :https config… I tried adding keys for :verify and :verify_fun to my https options (along with the function definitions):

verify: :verify_peer,
verify_fun: {&MyApp.verify_fun_selfsigned_cert/3, []}

but that didn’t seem to have any affect.

The other thing that might be relevant here is that when I serve the site locally over SSL, the first request is very slow – it takes maybe 15 or 20 seconds to get a response (with the TLS info). After that first request, things seem to work normally.

Might this be something to do with the version of Erlang?

Erlang/OTP 24 [erts-12.1.5] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1]
Elixir 1.13.4 (compiled with Erlang/OTP 24)

Any ideas appreciated!