Configure TLS CipherSuites and CurvePreferences

[akhilnittala]

Overview

TLS Ciphersuites are hardcoded currently, to meet the platform side compliance ciphersuites needs to be configureable, so made changes for tls ciphersuites and curve preferences to be configurable for web.

What this PR does / why we need it

Configures the tls ciphersuites and curvepreferences based on the parameters in config.yaml

Fixes: #4913

[Copilot]

Pull request overview

This PR makes the HTTPS listener’s TLS configuration more flexible by allowing operators to configure cipher suites (and curve preferences) from the web section of the config file, instead of relying on a fixed hardcoded list.

Changes:

• Add web.allowedTLSCiphers to configure the tls.Config.CipherSuites used by the HTTPS endpoint.
• Add parseCipherSuites helper plus unit tests for cipher-suite name parsing.
• Add web.allowedCurvePreferences and wire it into tls.Config.CurvePreferences.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
cmd/dex/serve.go	Reads new web TLS settings, builds tls.Config accordingly, and adds parseCipherSuites.
cmd/dex/serve_test.go	Adds unit tests for parseCipherSuites.
cmd/dex/config.go	Extends the Web config struct with new TLS configuration fields.

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[akhilnittala]

@nabokihms @sagikazarmark could you please help me in review process.