Today SPIRE Agent has logs for FetchX509SVID results for:

• No Identity Issued, Identity Issued, and errors in between.
• Discovered selectors

However the discovered selectors and identity decision are separate log entries, which makes debugging a bit more difficult than it needs it be, especially in the case of "No Identity Issued":

• two separate logs must be found to see the result and what was discovered about the caller
• if there are many parallel callers, it is difficult to associate results with selectors

Adding selectors as a log field to the logger passed in here (and potentially other parts of this package) could add clarity for operators.

Potentially this could mean that the existing discovered selectors log becomes redundant and could be removed, though it is already Debug level.