adds imds_available check

[tomjemmett]

before trying to get a managed token, perform a check to see if the endpoint is available. this times out significantly quicker than the get_managed_token function, and caches the result in an environment variable for future use

[Copilot]

Pull request overview

This PR adds a fast “IMDS available” probe before attempting managed-identity authentication, aiming to avoid the longer timeout path when running outside Azure and to cache the result for subsequent calls.

Changes:

• Gate the managed-token attempt in get_auth_token() behind a new imds_available() check.
• Introduce imds_available() (with generated documentation) that probes the IMDS/MSI endpoint and caches the result in IMDS_AVAILABLE.
• Minor formatting alignment in the get_auth_token() examples/docs.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 4 comments.

File	Description
R/get_auth_token.R	Adds imds_available() and uses it to gate managed-token retrieval in get_auth_token().
man/imds_available.Rd	New documentation page for imds_available().
man/get_auth_token.Rd	Example indentation/formatting adjustment.

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[francisbarton]

Please can you have a think about the comment - I'm not demanding a change but it might make sense to add in a defensive line somewhere.

[francisbarton]

Thanks!

[tomjemmett]

@francisbarton I've switched from as.logical to something a bit more defensive

[Copilot]

Pull request overview

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

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