feat(modules/blockchain_connector): introduce APIs for signing/verifying messages

lib/modules/blockchain_connector/index.js

@@ -388,6 +388,35 @@ class BlockchainConnector {
         res.send(JSON.stringify(this.contractsEvents));
       }
     );
+
+    plugin.registerAPICall(
+      'post',
+      '/embark-api/messages/sign',
+      (req, res) => {
+        const signer = req.body.address;
+        const message = req.body.message;
+        this.web3.eth.personal.sign(message, signer).then(signature => {
+          res.send({signer, signature, message})
+        }).catch(e => res.send({ error: e.message }))
+      }
+    );
+
+    plugin.registerAPICall(
+      'post',
+      '/embark-api/messages/verify',
+      (req, res) => {
+        let signature;
+        try {
+          signature = JSON.parse(req.body.message);
+        } catch(e) {
+          return res.send({ error: e.message });
+        }
+
+        this.web3.eth.personal.ecRecover(signature.message, signature.signature)
+          .then(address => res.send({address}))
+          .catch(e => res.send({ error: e.message }));
+      }
+    );
   }
 
   getAccountsWithTransactionCount(callback) {