fix(content-server): Fix issue on login with legacy accounts

Because:
- There was a regression in the last maintenance sprint when removing the ecosystemAnonId.

This Commit:
- Adds a collection of ​​DEPRECATED_KEYS that represent keys which may exist on legacy account data and need to be gracefully removed.
- Adds a test to make sure that a known deprecated field is handled and does not result in an error state.
- Adds a test to make sure that errors are still thrown for invalid keys.

packages/fxa-content-server/app/scripts/models/account.js

@@ -80,6 +80,7 @@ const DEFAULTS = _.extend(
 
 const ALLOWED_KEYS = Object.keys(DEFAULTS);
 const ALLOWED_PERSISTENT_KEYS = Object.keys(PERSISTENT);
+const DEPRECATED_KEYS = ['ecosystemAnonId'];
 
 const CONTENT_SERVER_OAUTH_SCOPE = 'profile profile:write clients:write';
 
@@ -651,7 +652,7 @@ const Account = Backbone.Model.extend(
           ) {
             updatedSessionData.email = options.originalLoginEmail;
           }
-          
+
           // We don't really need this value other than in login flow, it can
           // sometimes cause issues when user switches primary email
           this.unset('originalLoginEmail');
@@ -1022,6 +1023,16 @@ const Account = Backbone.Model.extend(
 
         // eslint-disable-next-line no-unused-vars
         for (const key in attributes) {
+          // As fields are phased out and no longer needed, they may drop out
+          // of the set of ALLOWED_KEYS. In this case, we should no longer store
+          // or use the associated key; however, it may still exist in a client's
+          // cached state (e.g. in local storage). The following ensures that
+          // deprecated keys are cleaned up over time.
+          if (_.contains(DEPRECATED_KEYS, key)) {
+            delete attributes[key];
+            continue;
+          }
+
           if (!_.contains(ALLOWED_KEYS, key)) {
             throw new Error(key + ' cannot be set on an Account');
           }

packages/fxa-content-server/app/tests/spec/models/user.js

@@ -126,6 +126,27 @@ describe('models/user', function () {
       });
   });
 
+  it('will not create invalid account', function () {
+    assert.throws(() => {
+      user.initAccount({
+        email: EMAIL,
+        boom: 'yes',
+      });
+    }, 'boom cannot be set on an Account');
+  });
+
+  it('will handles deprecated settings account', function () {
+    const account = user.initAccount({
+      email: EMAIL,
+      ecosystemAnonId: '123',
+    });
+
+    assert.equal(account.get('email'), EMAIL);
+    assert.deepEqual(account.pick('email'), { email: EMAIL });
+    assert.equal(account._notifier, notifier);
+    assert.notExists(account.ecosystemAnonId);
+  });
+
   describe('sessionStatus', () => {
     it('checks passed in account', () => {
       const account = user.initAccount({