Support configuration of spiffe-helper via environment variables

[eminwux]

When using spiffe-helper as a sidecar container, configuring it via environment variables provides greater flexibility and simplifies deployment.

The preliminary consensuated solution is to use the cleanenv library with support for JSON+YAML configuration formats.

To maintain backward compatibility:

• --config should be added for the new configuration format.
• --legacy-config should be used for HCL legacy configuration.

Behavior:

• When using --config, environment variables should override configurations in the new configuration files.
• When using --legacy-config, environment variables should only affect the HCL configuration file.

Deprecation Plan:

• Display deprecation warning messages for HCL configuration files in upcoming releases, until the next major version.
• Completely remove HCL configuration support in next major version.

For more context, see the Slack thread.
For a comparison of options, see pros and cons.

[eminwux]

I’m currently working on this.

[eminwux]

@kfox1111 @MarcosDY @faisal-memon

[faisal-memon]

Thanks @eminwux. Will you be using clean env?

[eminwux]

Thanks @eminwux. Will you be using clean env?

Hi @faisal-memon! Yes, I plan to use cleanenv. I’ll attach a draft PR once I’ve made significant progress.

[faisal-memon]

Sounds good @eminwux