Add support for jwt secret auth

[Dzejkop]

Description

Adds support for providing a JWT secret to auth against the provided RPC url.

Also fixes an inverted if statement

Testing

Tested manually

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2

[Dzejkop]

The original logic here was inverted. This line

			chainIDBig, ok := new(big.Int).SetString(chainID, 10)

would be executed if chainId was equal to empty string. Hence this drive-by fix

[cb-heimdall]

Review Error for meyer9 @ 2026-01-02 17:55:58 UTC
User failed mfa authentication, see go/mfa-help