Sign content and signature validation using new util method

[sadilchamishka]

Purpose

$subject

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 39.34%. Comparing base (7b8d07d) to head (cb7e045).
Report is 5 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #197      +/-   ##
============================================
+ Coverage     39.30%   39.34%   +0.04%     
  Complexity      405      405              
============================================
  Files           111      111              
  Lines          3608     3604       -4     
  Branches        410      410              
============================================
  Hits           1418     1418              
+ Misses         2034     2030       -4     
  Partials        156      156              

Flag	Coverage Δ
unit	43.09% <ø> (ø)

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[jenkins-is-staging]

PR builder started
Link: https://github.com/wso2/product-is/actions/runs/12175680284

[jenkins-is-staging]

PR builder completed
Link: https://github.com/wso2/product-is/actions/runs/12175680284
Status: failure

[jenkins-is-staging]

PR builder started
Link: https://github.com/wso2/product-is/actions/runs/12175939214

[jenkins-is-staging]

PR builder completed
Link: https://github.com/wso2/product-is/actions/runs/12175939214
Status: success

[jenkins-is-staging]

Approving the pull request based on the successful pr build https://github.com/wso2/product-is/actions/runs/12175939214