feat(server): allowed hosts

[james-d-elliott]

This implements an allowed hosts middleware which helps prevent communication with Authelia via unknown host headers.

[authelia]

Artifacts

These changes are published for testing on Buildkite, DockerHub and GitHub Container Registry.

Docker Container

• docker pull authelia/authelia:feat-host-header
• docker pull ghcr.io/authelia/authelia:feat-host-header

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[codecov]

Codecov Report

Merging #3680 (9e7c83e) into master (32d2815) will increase coverage by 0.04%.
The diff coverage is 87.75%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3680      +/-   ##
==========================================
+ Coverage   68.90%   68.95%   +0.04%     
==========================================
  Files         257      258       +1     
  Lines       16184    16215      +31     
  Branches      431      431              
==========================================
+ Hits        11152    11181      +29     
- Misses       4337     4340       +3     
+ Partials      695      694       -1     

Flag	Coverage Δ
backend	69.94% <87.75%> (+0.08%)	⬆️
frontend	62.13% <ø> (-0.25%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
internal/handlers/response.go	56.77% <ø> (-1.87%)	⬇️
internal/server/asset.go	69.75% <0.00%> (ø)
internal/server/handlers.go	92.06% <66.66%> (+0.08%)	⬆️
internal/handlers/handler_status.go	100.00% <100.00%> (ø)
internal/middlewares/allowed_hosts.go	100.00% <100.00%> (ø)
internal/middlewares/metrics.go	100.00% <100.00%> (ø)
internal/middlewares/util.go	77.77% <100.00%> (-22.23%)	⬇️
internal/middlewares/wrap.go	100.00% <100.00%> (ø)
internal/utils/strings.go	96.55% <100.00%> (+0.12%)	⬆️
... and 4 more

[nightah]

Only a couple of minor nits.

[nightah]

LGTM.