remove usage of request in generate token methods

[nurali-techie]

• remove usage of http request in method GenerateUnsignedUserAccessTokenForIdentity(). Such method ideally no need to have request in given context. Out of http request only AuthServiceURL is extracted which is now taken from config.GetAuthServiceURL()

• introduce new method ReplaceDomainPrefixInAbsoluteURLStr() in rest package, which works upon URL string input and does similar to what ReplaceDomainPrefixInAbsoluteURL() doing.

• config.GetAuthServiceURL() return http://auth.localhost instead of http://localhost for default case when it called from localhost while running test. We need to add auth sub-domain so that GenerateUnsignedUserAccessTokenForIdentity() test run smoothly. Also, auth_service_url will be always having sub-domain (in prod and prod-preview) and this change will make things consistent.

[codecov[bot]]

Codecov Report

Merging #861 into master will increase coverage by 0.06%. The diff coverage is 80%.

@@            Coverage Diff             @@
##           master     #861      +/-   ##
==========================================
+ Coverage    77.9%   77.96%   +0.06%     
==========================================
  Files         100      100              
  Lines        9824     9817       -7     
==========================================
+ Hits         7653     7654       +1     
+ Misses       1600     1596       -4     
+ Partials      571      567       -4

Impacted Files	Coverage Δ
authorization/token/manager/token_manager.go	83.35% <100%> (+1.45%)	:arrow_up:
configuration/configuration.go	81.9% <100%> (ø)	:arrow_up:
rest/rest.go	83.33% <57.14%> (-6.33%)	:arrow_down:

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[nurali-techie]

@xcoulon thanks for review :-)