Use "rest/api/3/myself" to retrieve JIRA profile details, not "rest/auth/1/session"

Summary:
Ref T13493. At time of writing, the old API method no longer functions: `1/session` does not return an `accountId` but all calls now require one.

Use the modern `3/myself` API instead. The datastructure returned by `2/user` (older appraoch) and `3/myself` (newer approach) is more or less the same, as far as I can tell.

Test Plan: Linked an account against modern-at-time-of-writing Atlassian-hosted JIRA.

Maniphest Tasks: T13493

Differential Revision: https://secure.phabricator.com/D21170

src/applications/auth/adapter/PhutilJIRAAuthAdapter.php

@@ -10,7 +10,6 @@ final class PhutilJIRAAuthAdapter extends PhutilOAuth1AuthAdapter {
 
   private $jiraBaseURI;
   private $adapterDomain;
-  private $currentSession;
   private $userInfo;
 
   public function setJIRABaseURI($jira_base_uri) {
@@ -106,23 +105,36 @@ final class PhutilJIRAAuthAdapter extends PhutilOAuth1AuthAdapter {
 
   private function getUserInfo() {
     if ($this->userInfo === null) {
-      $this->currentSession = $this->newJIRAFuture('rest/auth/1/session', 'GET')
+      $this->userInfo = $this->newUserInfo();
+    }
+
+    return $this->userInfo;
+  }
+
+  private function newUserInfo() {
+    // See T13493. Try a relatively modern (circa early 2020) API call first.
+    try {
+      return $this->newJIRAFuture('rest/api/3/myself', 'GET')
+        ->resolveJSON();
+    } catch (Exception $ex) {
+      // If we failed the v3 call, assume the server version is too old
+      // to support this API and fall back to trying the older method.
+    }
+
+    $session = $this->newJIRAFuture('rest/auth/1/session', 'GET')
       ->resolveJSON();
 
     // The session call gives us the username, but not the user key or other
     // information. Make a second call to get additional information.
 
     $params = array(
-        'username' => $this->currentSession['name'],
+      'username' => $session['name'],
     );
 
-      $this->userInfo = $this->newJIRAFuture('rest/api/2/user', 'GET', $params)
+    return $this->newJIRAFuture('rest/api/2/user', 'GET', $params)
       ->resolveJSON();
   }
 
-    return $this->userInfo;
-  }
-
   public static function newJIRAKeypair() {
     $config = array(
       'digest_alg' => 'sha512',