add cli command: account sign-data

Allow the signature of arbitrary data

references: #261

aeternity/__main__.py

@@ -414,6 +414,26 @@ def account_sign(keystore_name, password, network_id, unsigned_transaction, json
     except Exception as e:
         _print_error(e, exit_code=1)
 
+
+@account.command('sign-data', help="Sign arbitrary data")
+@click.argument('keystore_name', required=True)
+@click.argument('data', required=True)
+@global_options
+@account_options
+def account_sign_data(keystore_name, password, data, json_):
+    try:
+        set_global_options(json_)
+        account, _ = _account(keystore_name, password=password)
+        # force offline mode for the node_client
+        signature = encode(SIGNATURE, account.sign(data.encode('utf-8')))
+        # _print_object(txu, title='unsigned transaction')
+        _print_object({
+            "account": account.get_address(),
+            "signature": signature
+        }, title="data signature")
+    except Exception as e:
+        _print_error(e, exit_code=1)
+
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