This fix tries to address the issue in #22244 where the remote
API `/auth` will not set the default value of `serveraddress`
if not provided. This behavior happens after only in 1.11.0
and is a regression as in 1.10.3 `serveraddress` will be assigned
with `IndexServer` if no value is provided.
The default value `IndexServer` is assigned to `serveraddress` if
no value provided in this fix.
An integration test `TestAuthApi` has been added to cover this change
This fix fixes#22244.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
