feat: allow subaccount_sign to be called with provided user_ed_sk

Author: Bilb

include/session/config/groups/keys.hpp

@@ -491,6 +491,12 @@ class Keys : public ConfigSig {
             std::span<const unsigned char> signing_value,
             bool binary = false) const;
 
+    static Keys::swarm_auth swarm_subaccount_sign_as_user(
+            std::span<const unsigned char> user_ed25519_sk,
+            std::span<const unsigned char> msg,
+            std::span<const unsigned char> sign_val,
+            bool binary = false);
+
     /// API: groups/Keys::swarm_subaccount_token
     ///
     /// Constructs the subaccount token for a session id.  The main use of this is to submit a swarm

src/config/groups/keys.cpp

@@ -653,16 +653,15 @@ std::vector<unsigned char> Keys::swarm_subaccount_token(
     return out;
 }
 
-Keys::swarm_auth Keys::swarm_subaccount_sign(
+Keys::swarm_auth Keys::swarm_subaccount_sign_as_user(
+        std::span<const unsigned char> user_ed25519_sk,
         std::span<const unsigned char> msg,
         std::span<const unsigned char> sign_val,
         bool binary) const {
+
     if (sign_val.size() != 100)
         throw std::logic_error{"Invalid signing value: size is wrong"};
 
-    if (!_sign_pk)
-        throw std::logic_error{"Unable to verify: group pubkey is not set (!?)"};
-
     Keys::swarm_auth result;
     auto& [token, sub_sig, sig] = result;
 
@@ -775,6 +774,14 @@ Keys::swarm_auth Keys::swarm_subaccount_sign(
     return result;
 }
 
+Keys::swarm_auth Keys::swarm_subaccount_sign(
+        std::span<const unsigned char> msg,
+        std::span<const unsigned char> sign_val,
+        bool binary) const {
+    auto user_ed25519_sk_buf = this->user_ed25519_sk.data();
+    return Keys::swarm_subaccount_sign_as_user(user_ed25519_sk_buf, msg, sign_val, binary);
+}
+
 bool Keys::swarm_verify_subaccount(
         std::span<const unsigned char> sign_val, bool write, bool del) const {
     if (!_sign_pk)