Erlang error bad key length

[Copser]

Hello @mweibel, first awesome library, I'm using it on some of my projects, now I have tried to update our staging project and tried the new Erlang 24 and Elixir 12 but I had a problem with the library so I have started poking around.

First I have reverted back to Erlang 23 and Elixir 10.4 run the mix test and saw this

Generated credo app
==> facebook
Compiling 6 files (.ex)
Generated facebook app
...............................

  1) test signing decode (FacebookTest)
     test/facebook_test.exs:543
     ** (ErlangError) Erlang error: {:badarg, {'mac.c', 231}, 'Bad key length'}
     code: }} = Facebook.decode_signed_request(signed_request)
     stacktrace:
       (crypto 4.9) :crypto.mac_nif(:poly1305, :sha256, "456", "eyJpZCI6IjExNjM5NzMwMzg2NTk2In0=")
       (facebook 0.24.0) lib/facebook.ex:825: Facebook.decode_signed_request/1
       test/facebook_test.exs:550: (test)



  2) test fan_count success (FacebookTest)
     test/facebook_test.exs:252
     ** (ErlangError) Erlang error: {:badarg, {'mac.c', 231}, 'Bad key length'}
     code: Facebook.fan_count(
     stacktrace:
       (crypto 4.9) :crypto.mac_nif(:poly1305, :sha256, "456", "123|456")
       (facebook 0.24.0) lib/facebook.ex:895: Facebook.signature_base16/1
       (facebook 0.24.0) lib/facebook.ex:904: Facebook.add_app_secret/2
       (facebook 0.24.0) lib/facebook.ex:417: Facebook.get_object/3
       test/facebook_test.exs:256: (test)

.

  3) test fan_count error (FacebookTest)
     test/facebook_test.exs:263
     ** (ErlangError) Erlang error: {:badarg, {'mac.c', 231}, 'Bad key length'}
     code: assert {:error, _} = Facebook.fan_count(@page_id, invalid_access_token)
     stacktrace:
       (crypto 4.9) :crypto.mac_nif(:poly1305, :sha256, "456", "123")
       (facebook 0.24.0) lib/facebook.ex:895: Facebook.signature_base16/1
       (facebook 0.24.0) lib/facebook.ex:904: Facebook.add_app_secret/2
       (facebook 0.24.0) lib/facebook.ex:417: Facebook.get_object/3
       test/facebook_test.exs:265: (test)



  4) test publish feed - success (FacebookTest)
     test/facebook_test.exs:124
     ** (ErlangError) Erlang error: {:badarg, {'mac.c', 231}, 'Bad key length'}
     code: Facebook.publish(
     stacktrace:
       (crypto 4.9) :crypto.mac_nif(:poly1305, :sha256, "456", "123")
       (facebook 0.24.0) lib/facebook.ex:895: Facebook.signature_base16/1
       (facebook 0.24.0) lib/facebook.ex:904: Facebook.add_app_secret/2
       (facebook 0.24.0) lib/facebook.ex:215: Facebook.publish/4
       test/facebook_test.exs:128: (test)



  5) test get_object error (FacebookTest)
     test/facebook_test.exs:282
     ** (ErlangError) Erlang error: {:badarg, {'mac.c', 231}, 'Bad key length'}
     code: assert {:error, _} = Facebook.get_object("1234567", invalid_access_token)
     stacktrace:
       (crypto 4.9) :crypto.mac_nif(:poly1305, :sha256, "456", "123")
       (facebook 0.24.0) lib/facebook.ex:895: Facebook.signature_base16/1
       (facebook 0.24.0) lib/facebook.ex:904: Facebook.add_app_secret/2
       (facebook 0.24.0) lib/facebook.ex:417: Facebook.get_object/3
       test/facebook_test.exs:284: (test)



  6) test signing payload (FacebookTest)
     test/facebook_test.exs:536
     ** (ErlangError) Erlang error: {:badarg, {'mac.c', 231}, 'Bad key length'}
     code: Facebook.sign(payload)
     stacktrace:
       (crypto 4.9) :crypto.mac_nif(:poly1305, :sha256, "456", "eyJpZCI6IjExNjM5NzMwMzg2NTk2In0=")
       (facebook 0.24.0) lib/facebook.ex:890: Facebook.signature_base64/1
       (facebook 0.24.0) lib/facebook.ex:837: Facebook.sign/1
       test/facebook_test.exs:540: (test)

....

  7) test page feed success (FacebookTest)
     test/facebook_test.exs:396
     ** (ErlangError) Erlang error: {:badarg, {'mac.c', 231}, 'Bad key length'}
     code: Facebook.page_feed(
     stacktrace:
       (crypto 4.9) :crypto.mac_nif(:poly1305, :sha256, "456", "123|456")
       (facebook 0.24.0) lib/facebook.ex:895: Facebook.signature_base16/1
       (facebook 0.24.0) lib/facebook.ex:904: Facebook.add_app_secret/2
       (facebook 0.24.0) lib/facebook.ex:440: Facebook.get_object_edge/4
       test/facebook_test.exs:400: (test)



  8) test object count success (FacebookTest)
     test/facebook_test.exs:430
     ** (ErlangError) Erlang error: {:badarg, {'mac.c', 231}, 'Bad key length'}
     code: Facebook.object_count(
     stacktrace:
       (crypto 4.9) :crypto.mac_nif(:poly1305, :sha256, "456", "123")
       (facebook 0.24.0) lib/facebook.ex:895: Facebook.signature_base16/1
       (facebook 0.24.0) lib/facebook.ex:904: Facebook.add_app_secret/2
       (facebook 0.24.0) lib/facebook.ex:534: Facebook.object_count/3
       test/facebook_test.exs:434: (test)

....

Finished in 13.9 seconds
48 tests, 8 failures

Randomized with seed 864838

I have changes the app_id and app_secret to more let's say "realistic" string and fix the tests, I have also changed the deprecated load_file to require_file in test_helper. Tests are also passing on Erlang 24.0.5/Elixir 1.12.3-otp-24 versions.

Is this something you will be interested in merging if it meets your criteria?