Do not set JsonWebToken.SigningKey until signature succeeds

[iNinja]

Do not set JsonWebToken.SigningKey until signature succeeds

• Set the SigningKey in JsonWebToken only after the signature has been validated.
• Added test to prevent regressions

Fixes #3109

[github-actions]

Summary

Summary

Generated on:	1/30/2025 - 11:25:21 PM
Coverage date:	1/30/2025 - 11:15:41 PM - 1/30/2025 - 11:24:54 PM
Parser:	MultiReport (60x Cobertura)
Assemblies:	1
Classes:	7
Files:	2
Line coverage:	80.3% (620 of 772)
Covered lines:	620
Uncovered lines:	152
Coverable lines:	772
Total lines:	483
Branch coverage:	67.8% (228 of 336)
Covered branches:	228
Total branches:	336
Method coverage:	Feature is only available for sponsors

Coverage

Microsoft.IdentityModel.JsonWebTokens - 80.3%

Name	Line	Branch
Microsoft.IdentityModel.JsonWebTokens	80.3%	67.8%
Microsoft.IdentityModel.JsonWebTokens.JwtTokenUtilities	100%
System.Text.RegularExpressions.Generated	80.3%	67.8%
System.Text.RegularExpressions.Generated	80.3%	67.8%
System.Text.RegularExpressions.Generated.<RegexGenerator_g>F12A1AEDDDFE32BA DF4DBFF323AF1BCB48B9F9721B7CD3E05F5E034CF225E3DF8__CreateJweRegex_1	79.2%	68%
System.Text.RegularExpressions.Generated.<RegexGenerator_g>F12A1AEDDDFE32BA DF4DBFF323AF1BCB48B9F9721B7CD3E05F5E034CF225E3DF8__CreateJwsRegex_0	81.4%	67.6%
System.Text.RegularExpressions.Generated.<RegexGenerator_g>F334844C618E00D3 CEC5D3FE0D00CF0141BBEE98635313BB2CB8D3921464CE05A__CreateJweRegex_1	79.2%	68%
System.Text.RegularExpressions.Generated.<RegexGenerator_g>F334844C618E00D3 CEC5D3FE0D00CF0141BBEE98635313BB2CB8D3921464CE05A__CreateJwsRegex_0	81.4%	67.6%