acme: update contact information before getting a cert

part of #544

there were two approaches considered:
1. pipe through owner email from appstore. this requires to save this
   value in settingsdb and we need to remember this in case user changes
   the email. another issue is that selfhost installer tooling needs to
   require this new value.

2. simply update owner email each time. this is the chosen approach.

src/cert/acme.js

@@ -125,6 +125,29 @@ Acme.prototype.sendSignedRequest = function (url, payload, callback) {
     });
 };
 
+Acme.prototype.updateContact = function (registrationUri, callback) {
+    assert.strictEqual(typeof registrationUri, 'string');
+    assert.strictEqual(typeof callback, 'function');
+
+    debug('updateContact: %s %s', registrationUri, this.email);
+
+    // https://github.com/ietf-wg-acme/acme/issues/30
+    var payload = {
+        resource: 'reg',
+        contact: [ 'mailto:' + this.email ],
+        agreement: LE_AGREEMENT
+    };
+
+    this.sendSignedRequest(registrationUri, JSON.stringify(payload), function (error, result) {
+        if (error) return callback(new AcmeError(AcmeError.EXTERNAL_ERROR, 'Network error when registering user: ' + error.message));
+        if (result.statusCode !== 200) return callback(new AcmeError(AcmeError.EXTERNAL_ERROR, util.format('Failed to update contact. Expecting 200, got %s %s', result.statusCode, result.text)));
+
+        debug('updateContact: contact of user updated to %s', this.email);
+
+        callback();
+    });
+};
+
 Acme.prototype.registerUser = function (callback) {
     assert.strictEqual(typeof callback, 'function');
 
@@ -136,14 +159,15 @@ Acme.prototype.registerUser = function (callback) {
 
     debug('registerUser: %s', this.email);
 
+    var that = this;
     this.sendSignedRequest(this.caOrigin + '/acme/new-reg', JSON.stringify(payload), function (error, result) {
         if (error) return callback(new AcmeError(AcmeError.EXTERNAL_ERROR, 'Network error when registering user: ' + error.message));
-        if (result.statusCode === 409) return callback(new AcmeError(AcmeError.ALREADY_EXISTS, result.body.detail));
+        if (result.statusCode === 409) return that.updateContact(result.headers.location, callback); // already exists
         if (result.statusCode !== 201) return callback(new AcmeError(AcmeError.EXTERNAL_ERROR, util.format('Failed to register user. Expecting 201, got %s %s', result.statusCode, result.text)));
 
         debug('registerUser: registered user %s', this.email);
 
-        callback();
+        callback(null);
     });
 };
 
@@ -362,7 +386,7 @@ Acme.prototype.acmeFlow = function (domain, callback) {
 
     var that = this;
     this.registerUser(function (error) {
-        if (error && error.reason !== AcmeError.ALREADY_EXISTS) return callback(error);
+        if (error) return callback(error);
 
         that.registerDomain(domain, function (error, result) {
             if (error) return callback(error);