Horizon sessions do not properly observe SESSION_TIMEOUT

[chenyujie]

Refer to Bug-fix #1562452:
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This calculation uses the 'token_life' var which is a
datetime.timedelta object. timedelta.seconds gets us just the
'seconds' component of the object, truncating away any days, hours,
or weeks that might be included in the object.

What we want here is the total time in seconds, which is
total_seconds().
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It is fixed in master branch and released in 2.3.0, but mitaka branch still have the same problem.

When keystone token lifetime larger than 1 day, such as 5 days, the problem would appear frequently and nothing can be done on horizon because login is required on almost every action.

[David Lyle (david-lyle)]

would require backport to mitaka stable branch, is the severe enough to warrant the backport?

[Launchpad Janitor (janitor)]

[Expired for django-openstack-auth because there has been no activity for 60 days.]