Use a named location for authSignURL

[aledbf]

What this PR does / why we need it:

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

[k8s-ci-robot]

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[codecov-io]

Codecov Report

Merging #4859 into master will decrease coverage by 0.06%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #4859      +/-   ##
==========================================
- Coverage   58.46%   58.39%   -0.07%     
==========================================
  Files          88       88              
  Lines        6719     6720       +1     
==========================================
- Hits         3928     3924       -4     
- Misses       2362     2367       +5     
  Partials      429      429

Impacted Files	Coverage Δ
internal/ingress/controller/template/template.go	79.51% <50%> (-0.73%)	⬇️

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[aledbf]

/retest

[aledbf]

/retest

[abergmann]

CVE-2019-20372 was assigned to this issue.