fix(clone): a CodeCommit region borrows saved key IDs; Clone runs in the background

An IAM SSH key ID logs in to every region of its AWS account, but a login
was saved per host, so a repo in a region with no key ID of its own was
refused. Clone now tries the key IDs saved for the other CodeCommit regions
(each with its own key; the first ls-remote accepts, or the only one) and
keeps that user in the clone's origin.

Files → New → Clone repository steps aside for its progress chip as soon
as the clone starts; a failure asking for a login reopens the form.

server/__tests__/git-clone.test.js

@@ -5,7 +5,7 @@
  * ECREDENTIALS for a remote wanting a login), `/api/me/git` (key made once,
  * only the public half returned, 0600 on disk; named keys beside the default
  * ones, SSH logins per alias tied to one key, which a clone then offers
- * alone), and the member (S3) path of
+ * alone; a CodeCommit region with no login borrowing another region's), and the member (S3) path of
  * `server/lib/git-identity.js` with run-as and git stubbed — what reaches
  * git's argv, and that a login typed without "remember" leaves the member's
  * store as it was.
@@ -650,6 +650,44 @@ describe("several accounts: named keys and SSH logins per alias", () => {
   });
 });
 
+describe("CodeCommit: a region with no login borrows another region's", () => {
+  it("clones as the first saved CodeCommit user the remote accepts, and keeps that user in origin", async () => {
+    const bare = path.join(ROOT, "bare.git");
+    const R = "git-codecommit.ap-southeast-2.amazonaws.com";
+    const saved = [
+      ["git-codecommit.ap-southeast-1.amazonaws.com", "APKAONE"],
+      ["git-codecommit.us-east-1.amazonaws.com", "APKATWO"],
+    ];
+    for (const [host, user] of saved) {
+      assert.equal((await request("PUT", "/api/me/git/ssh-user", { host, user })).status, 200);
+    }
+    // The test forge stands in for the region: APKAONE is refused (no such
+    // repo behind it), APKATWO is the account that owns the repo.
+    const rules = [
+      [`url.file://${ROOT}/nowhere.git.insteadOf`, `ssh://APKAONE@${R}/v1/repos/r`],
+      [`url.file://${bare}.insteadOf`, `ssh://APKATWO@${R}/v1/repos/r`],
+    ];
+    for (const [k, v] of rules) execFileSync("git", ["config", "--global", "--add", k, v]);
+    try {
+      const r = await request("POST", "/api/lanes/clone", {
+        url: `ssh://${R}/v1/repos/r`,
+        parent: WORK,
+        name: "borrowed-login",
+      });
+      assert.equal(r.status, 201, JSON.stringify(r.body));
+      const origin = execFileSync(
+        "git",
+        ["-C", path.join(WORK, "borrowed-login"), "config", "remote.origin.url"],
+        { encoding: "utf8" }
+      ).trim();
+      assert.equal(origin, `ssh://APKATWO@${R}/v1/repos/r`);
+    } finally {
+      for (const [k] of rules) execFileSync("git", ["config", "--global", "--unset-all", k]);
+      for (const [host] of saved) await request("DELETE", `/api/me/git/ssh-user/${host}`);
+    }
+  });
+});
+
 describe("git-identity, member account (S3, stubbed)", () => {
   const runAs = require("../lib/run-as");
   const worktree = require("../lib/worktree");