Add SSL validation support for certs_keys

lib/plug/ssl.ex

@@ -169,6 +169,7 @@ defmodule Plug.SSL do
     |> check_for_missing_keys()
     |> validate_ciphers()
     |> normalize_ssl_files()
+    |> normalize_certs_keys_ssl_files()
     |> convert_to_charlist()
     |> set_secure_defaults()
     |> configure_managed_tls()
@@ -179,24 +180,45 @@ defmodule Plug.SSL do
   end
 
   defp check_for_missing_keys(options) do
+    has_certs_keys? = List.keymember?(options, :certs_keys, 0)
     has_sni? = List.keymember?(options, :sni_hosts, 0) or List.keymember?(options, :sni_fun, 0)
     has_key? = List.keymember?(options, :key, 0) or List.keymember?(options, :keyfile, 0)
     has_cert? = List.keymember?(options, :cert, 0) or List.keymember?(options, :certfile, 0)
 
     cond do
       has_sni? -> options
-      not has_key? -> fail("missing option :key/:keyfile")
-      not has_cert? -> fail("missing option :cert/:certfile")
+      not (has_key? or has_certs_keys?) -> fail("missing option :key/:keyfile/:certs_keys")
+      not (has_cert? or has_certs_keys?) -> fail("missing option :cert/:certfile/:certs_keys")
       true -> options
     end
   end
 
   defp normalize_ssl_files(options) do
     ssl_files = [:keyfile, :certfile, :cacertfile, :dhfile]
-    Enum.reduce(ssl_files, options, &normalize_ssl_file(&1, &2))
+    Enum.reduce(ssl_files, options, &normalize_ssl_file(&1, &2, options[:otp_app]))
   end
 
-  defp normalize_ssl_file(key, options) do
+  defp normalize_certs_keys_ssl_files(options) do
+    if certs_keys = options[:certs_keys] do
+      ssl_files = [:keyfile, :certfile]
+
+      updated_certs_keys =
+        Enum.map(certs_keys, fn cert_key ->
+          Enum.reduce(
+            ssl_files,
+            Map.to_list(cert_key),
+            &normalize_ssl_file(&1, &2, options[:otp_app])
+          )
+          |> Map.new()
+        end)
+
+      List.keystore(options, :certs_keys, 0, {:certs_keys, updated_certs_keys})
+    else
+      options
+    end
+  end
+
+  defp normalize_ssl_file(key, options, otp_app) do
     value = options[key]
 
     cond do
@@ -207,7 +229,7 @@ defmodule Plug.SSL do
         put_ssl_file(options, key, value)
 
       true ->
-        put_ssl_file(options, key, Path.expand(value, otp_app(options)))
+        put_ssl_file(options, key, Path.expand(value, resolve_otp_app(otp_app)))
     end
   end
 
@@ -225,9 +247,9 @@ defmodule Plug.SSL do
     List.keystore(options, key, 0, {key, value})
   end
 
-  defp otp_app(options) do
-    if app = options[:otp_app] do
-      Application.app_dir(app)
+  defp resolve_otp_app(otp_app) do
+    if otp_app do
+      Application.app_dir(otp_app)
     else
       fail("the :otp_app option is required when setting relative SSL certfiles")
     end

test/plug/ssl_test.exs

@@ -4,6 +4,17 @@ defmodule Plug.SSLTest do
   import Plug.Conn
 
   describe "configure" do
+    # make sure some dummy files used for the keyfile and certfile
+    # tests are removed after each test.
+    setup do
+      on_exit(fn ->
+        File.rm("_build/test/lib/plug/abcdef")
+        File.rm("_build/test/lib/plug/ghijkl")
+      end)
+
+      []
+    end
+
     import Plug.SSL, only: [configure: 1]
 
     test "sets secure_renegotiate and reuse_sessions to true depending on the version" do
@@ -97,6 +108,67 @@ defmodule Plug.SSLTest do
       assert {:cert, "ghijkl"} in opts
     end
 
+    test "fails to configure if keyfile and certfile aren't absolute paths and otp_app is missing" do
+      assert {:error, message} = configure([:inet6, keyfile: "abcdef", certfile: "ghijkl"])
+      assert message == "the :otp_app option is required when setting relative SSL certfiles"
+    end
+
+    test "fails to configure if the keyfile doesn't exist" do
+      assert {:error, message} =
+               configure([:inet6, keyfile: "abcdef", certfile: "ghijkl", otp_app: :plug])
+
+      assert message =~
+               ":keyfile either does not exist, or the application does not have permission to access it"
+    end
+
+    test "fails to configure if the certfile doesn't exist" do
+      File.touch("_build/test/lib/plug/abcdef")
+
+      assert {:error, message} =
+               configure([:inet6, keyfile: "abcdef", certfile: "ghijkl", otp_app: :plug])
+
+      assert message =~
+               ":certfile either does not exist, or the application does not have permission to access it"
+    end
+
+    test "expands the paths to the keyfile and certfile using the otp_app" do
+      File.touch("_build/test/lib/plug/abcdef")
+      File.touch("_build/test/lib/plug/ghijkl")
+
+      assert {:ok, opts} =
+               configure([:inet6, keyfile: "abcdef", certfile: "ghijkl", otp_app: :plug])
+
+      assert to_string(opts[:keyfile]) =~ "_build/test/lib/plug/abcdef"
+      assert to_string(opts[:certfile]) =~ "_build/test/lib/plug/ghijkl"
+    end
+
+    test "supports the certs_keys ssl config option" do
+      assert {:ok, opts} =
+               configure([:inet6, certs_keys: [%{key: "abcdef", cert: "ghijkl"}]])
+
+      assert :inet6 in opts
+      assert opts[:certs_keys] == [%{key: "abcdef", cert: "ghijkl"}]
+    end
+
+    test "expands the paths for keyfile and certfile in the certs_keys ssl config option" do
+      File.touch("_build/test/lib/plug/abcdef")
+      File.touch("_build/test/lib/plug/ghijkl")
+
+      assert {:ok, opts} =
+               configure([
+                 :inet6,
+                 certs_keys: [%{keyfile: "abcdef", certfile: "ghijkl"}],
+                 otp_app: :plug
+               ])
+
+      assert :inet6 in opts
+
+      [%{keyfile: keyfile, certfile: certfile}] = opts[:certs_keys]
+
+      assert to_string(keyfile) =~ "_build/test/lib/plug/abcdef"
+      assert to_string(certfile) =~ "_build/test/lib/plug/ghijkl"
+    end
+
     test "errors when an invalid cipher is given" do
       assert configure(key: "abcdef", cert: "ghijkl", cipher_suite: :unknown) ==
                {:error, "unknown :cipher_suite named :unknown"}