Add support for HMAC type to vault_transit_secret_backend_key

[roberteckert]

• Add key_size as it is necessary for HMAC. Default to 0 bits as that is the default for all key types except HMAC currently.

Description

This PR updates the vault_transit_secret_backend_key to accept the hmac key type along with the requisite key_size argument so that transit keys of the hmac type can be created.

Relates OR Closes #0000

Checklist

• Added CHANGELOG entry (only for user-facing changes)
• Acceptance tests where run against all supported Vault Versions

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccXXX'

...

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[hashicorp-cla]

All committers have signed the CLA.

[fairclothjm]

Thanks! Looking good so far! Had a few comments on checking the Vault server version.

Could we also add a Changelog entry under Unreleased?

[roberteckert]

Thanks for the feedback. I:

• Removed ValidateFunc to rely on Vault's internal validation
• Updated CHANGELOG.md
• Slightly tweaked the description of key_size
• Wrapped the data["key_size"] allocation in a check for Vault version
• Added SkipFunc blocks to the hmac tests

[fairclothjm]

LGTM! Thanks!

[roberteckert]

This seems done - is there anything else you require from me?

[fairclothjm]

We don't require anything else, thanks @roberteckert!