Symptoms:

When attempting to connect your Cloud site to Google Apps the integration fails with the following error.

Error getting user list from Google:
{
  "code" : 403,
  "errors" : [ {
    "domain" : "global",
    "message" : "Domain cannot use apis.",
    "reason" : "domainCannotUseApis"
  } ],
  "message" : "Domain cannot use apis."
}

Cause:

Your Google Apps domain is configured to disallow API access. Without this access Atlassian Cloud is unable to access the APIs that it requires in order to read user information from your domain.

Resolution

You need to enable the administrative APIs in the Google Apps Control Panel.