There's a headers parameter in the config object you pass to $http
for per-call headers:
$http({method: 'GET', url: 'www.google.com/someapi', headers: {
'Authorization': 'Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ=='}
});
Or with the shortcut method:
$http.get('www.google.com/someapi', {
headers: {'Authorization': 'Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ=='}
});
The list of the valid parameters is available in the $http service documentation.