On November 5, 2014 , we'll be sunsetting  the login  field in the ManagedCustomer  class. We understand this may impact your applications and are recommending the following options to account for this change:
Maintaining customer contacts 
You should not use the login field to manage your clients' contacts and email addresses. You should always maintain your own client contacts. If your application currently relies on the login field, you can use ManagedCustomerService.get()  to create a mapping between customer IDs and login emails before November 5, 2014 .
Identifying client accounts 
CustomerId  should be used instead of the login  field to uniquely identify an account. To provide a friendly name for an account, you can use the name  field. You may set the name  field when creating a new account using the ManagedCustomerServer.mutate()  method.
AdWords allows users to invite multiple users to manage their applications as well as change  their AdWords sign-in information. However, the login  field is not updated to reflect changes in AdWords sign-in information. So relying on the login field makes your application error prone if a user changes their AdWords sign-in information.
Determining the access level of a user 
Your application runs with the same access levels as the user whose OAuth2 access token you send in your API calls. To determine if a user is authorized to make a particular change, you can make API calls with the validateOnly  header set to true. If the user isn’t authorized to make changes, the call will fail with an AuthorizationError .
Login field information doesn't convey the access level the user has within AdWords. If you rely on a user’s login email to determine their access level, your application may run into errors if the user’s account access levels change.
If you have questions or feedback about this change, or encounter a use case we’ve missed, let us know on our developer forum  or Google+ page .