From 82d7d28f3f3440c7fade5284ee5724f895c3f36e Mon Sep 17 00:00:00 2001
From: Adolfo Builes <builes.adolfo@gmail.com>
Date: Fri, 19 Jul 2019 15:06:05 -0700
Subject: [PATCH]  Implement SEP0010 transaction challenge builder.

---
 src/index.ts            |  1 +
 src/utils.ts            | 51 +++++++++++++++++++++++++++++++++++++++++
 test/unit/utils_test.js | 45 ++++++++++++++++++++++++++++++++++++
 3 files changed, 97 insertions(+)
 create mode 100644 src/utils.ts
 create mode 100644 test/unit/utils_test.js

diff --git a/src/index.ts b/src/index.ts
index ad07af319..ddd2f8688 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -27,6 +27,7 @@ export {
   SERVER_TIME_MAP,
   getCurrentServerTime,
 } from "./horizon_axios_client";
+export * from "./utils";
 
 // expose classes and functions from stellar-base
 export * from "stellar-base";
diff --git a/src/utils.ts b/src/utils.ts
new file mode 100644
index 000000000..5132da980
--- /dev/null
+++ b/src/utils.ts
@@ -0,0 +1,51 @@
+import { randomBytes } from "crypto";
+import { Account, Keypair, Operation, TransactionBuilder } from "stellar-base";
+
+/**
+ * Collection on util functions
+ *
+ * @namespace Utils
+ */
+export namespace Utils {
+  /**
+   * Returns a valid SEP0010 challenge which you can use for Stellar Web Authentication.
+   *
+   * @see [SEP0010: Stellar Web Authentication](https://github.com/stellar/stellar-protocol/blob/master/ecosystem/sep-0010.md)
+   * @param {Keypair} serverKeypair Server's keypair.
+   * @param {string} clientAccountID Client's Stellar account.
+   * @param {string} anchorName.
+   * @param {number} [timeout=300] Challenge duration (default to 5 minutes).
+   */
+  export function buildChallengeTx(
+    serverKeypair: Keypair,
+    clientAccountID: string,
+    anchorName: string,
+    timeout: number = 300,
+  ): string {
+    const account = new Account(serverKeypair.publicKey(), "-1");
+    const now = Math.floor(Date.now() / 1000);
+
+    const transaction = new TransactionBuilder(account, {
+      fee: 100,
+      timebounds: {
+        minTime: now,
+        maxTime: now + timeout,
+      },
+    })
+      .addOperation(
+        Operation.manageData({
+          name: `${anchorName} auth`,
+          value: randomBytes(64),
+          source: clientAccountID,
+        }),
+      )
+      .build();
+
+    transaction.sign(serverKeypair);
+
+    return transaction
+      .toEnvelope()
+      .toXDR("base64")
+      .toString();
+  }
+}
diff --git a/test/unit/utils_test.js b/test/unit/utils_test.js
new file mode 100644
index 000000000..ef7357649
--- /dev/null
+++ b/test/unit/utils_test.js
@@ -0,0 +1,45 @@
+describe('Utils', function() {
+  describe('Utils.buildChallengeTx', function() {
+    it('returns challenge which follows SEP0010 spec', function() {
+      let keypair = StellarSdk.Keypair.random();
+
+      const challenge = StellarSdk.Utils.buildChallengeTx(
+        keypair,
+        "GBDIT5GUJ7R5BXO3GJHFXJ6AZ5UQK6MNOIDMPQUSMXLIHTUNR2Q5CFNF",
+        "SDF"
+      );
+
+      const transaction = new StellarSdk.Transaction(challenge);
+
+      expect(transaction.sequence).to.eql("0");
+      expect(transaction.source).to.eql(keypair.publicKey());
+      expect(transaction.operations.length).to.eql(1);
+
+      const { maxTime, minTime } = transaction.timeBounds;
+
+      expect(parseInt(maxTime) - parseInt(minTime)).to.eql(300);
+
+      const [ operation ] =  transaction.operations;
+
+      expect(operation.name).to.eql("SDF auth");
+      expect(operation.source).to.eql("GBDIT5GUJ7R5BXO3GJHFXJ6AZ5UQK6MNOIDMPQUSMXLIHTUNR2Q5CFNF");
+      expect(operation.type).to.eql("manageData");
+      expect(operation.value.length).to.eql(64);
+    });
+
+    it('uses the passed-in timeout', function() {
+      let keypair = StellarSdk.Keypair.random();
+
+      const challenge = StellarSdk.Utils.buildChallengeTx(
+        keypair,
+        "GBDIT5GUJ7R5BXO3GJHFXJ6AZ5UQK6MNOIDMPQUSMXLIHTUNR2Q5CFNF",
+        "SDF",
+        600
+      );
+
+      const transaction = new StellarSdk.Transaction(challenge);
+      const { maxTime, minTime } = transaction.timeBounds;
+      expect(parseInt(maxTime) - parseInt(minTime)).to.eql(600);
+    });
+  });
+});