Support in Erlang's SSL library for GRiSP's Secure Element without using OpenSSL crypto engines.

Usage:

    Key = #{algorithm => ecdsa, sign_fun => {my_module, my_sign_fun}}.

Then add {key, Key} to the SSL options (server and/or client possible). The sign_fun has arity one
and will get the to be signed Message (TLS 1.3) or {digest, Digest} (TLS 1.2), analogous to ssl:sign/3.
The intended use here is providing a callback for grisp_cryptoauth:sign/2. While this patch makes
heavy use of the existing infrastructure for crypto engines it is completely backwards compatible, e.g.
crypto engines still work.

diff --git a/lib/ssl/src/ssl_config.erl b/lib/ssl/src/ssl_config.erl
index 46578c05a5..c4e11622a6 100644
--- a/lib/ssl/src/ssl_config.erl
+++ b/lib/ssl/src/ssl_config.erl
@@ -104,6 +104,9 @@ group_pairs([#{private_key := #'DSAPrivateKey'{}} = Pair | Rest], #{dsa := DSA}
 group_pairs([#{private_key := #{algorithm := dss, engine := _}} = Pair | Rest], Group) ->
     Pairs = maps:get(dsa, Group),
     group_pairs(Rest, Group#{dsa => [Pair | Pairs]});
+group_pairs([#{private_key := #{algorithm := Alg, sign_fun := _}} = Pair | Rest], Group) ->
+    Pairs = maps:get(Alg, Group),
+    group_pairs(Rest, Group#{Alg => [Pair | Pairs]});
 group_pairs([#{private_key := #{algorithm := Alg, engine := _}} = Pair | Rest], Group) ->
     Pairs = maps:get(Alg, Group),
     group_pairs(Rest, Group#{Alg => [Pair | Pairs]}).
@@ -308,6 +311,9 @@ init_certificates(OwnCerts, _, _, _) when is_binary(OwnCerts)->
 init_certificates(OwnCerts, _, _, _) ->
     {ok, OwnCerts}.
 
+%% HACK: allow callbacks for signing using the GRiSP Secure Element
+init_private_key(_, #{algorithm := ecdsa, sign_fun := _SignFun} = Key, _, _, _) ->
+    Key;
 init_private_key(_, #{algorithm := Alg} = Key, _, _Password, _Client) when Alg == ecdsa;
                                                                            Alg == rsa;
                                                                            Alg == dss ->
diff --git a/lib/ssl/src/ssl_handshake.erl b/lib/ssl/src/ssl_handshake.erl
index 56a1ca81b9..8163c7640b 100644
--- a/lib/ssl/src/ssl_handshake.erl
+++ b/lib/ssl/src/ssl_handshake.erl
@@ -2121,6 +2121,12 @@ digitally_signed(Version, Msg, HashAlgo, PrivateKey, SignAlgo) ->
 	    throw(?ALERT_REC(?FATAL, ?HANDSHAKE_FAILURE, bad_key(PrivateKey)))
     end.
 
+%% HACK: allow callbacks for signing using the GRiSP Secure Element
+%% We only care here for sha256 + ecdsa for TLS 1.2 and 1.3 (SSL 3.3 and 3.4)
+do_digitally_signed({3, 4}, Msg, sha256, #{algorithm := ecdsa, sign_fun := {Mod, Fun}}, ecdsa) ->
+    Mod:Fun(Msg);
+do_digitally_signed({3, 3}, Hash, sha256, #{algorithm := ecdsa, sign_fun := {Mod, Fun}}, ecdsa) ->
+    Mod:Fun({digest, Hash});
 do_digitally_signed({3, Minor}, Msg, HashAlgo, {#'RSAPrivateKey'{} = Key,
                                                  #'RSASSA-PSS-params'{}}, SignAlgo) when Minor >= 3 ->
     Options = signature_options(SignAlgo, HashAlgo),