fix: redact access token in config command output - #787

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

Fixes #786.

Describe the solution you've provided

The stored access token was rendered verbatim by config --list and by the --set/--unset validation error. Two commits, one per path.

1. config --list. Adds Config.Redacted(), which returns a copy with sensitive values replaced by [REDACTED], and marshals that for output instead of the raw config. The plaintext renderer, --output json, and the JSON default used when stdout is not a terminal all derive from the same json.Marshal in cmd/config/config.go, so the single substitution covers all three.

Two details worth flagging for review:

• The receiver is a value, so the copy is free and nothing that is written back to disk is affected. Verified end to end: the config file is byte-identical after --list.
• An unset token is left empty rather than set to [REDACTED], so omitempty still elides the key. Reporting an absent token as "present but hidden" would be a worse answer than omitting it.

I chose an explicit method over reflecting on a new struct tag, or over unmarshalling to a map and substituting there. The map route re-sorts the keys and changes output shape for everyone; the method preserves field order and matches the hand-written switch already used in Update.

2. Validation errors. --set and --unset reject an unknown key by echoing it back. The argument in that position is not always a key — transposing --set <key> <value> puts the value there, and for access-token that value is a secret:

$ ldcli config --set api-<token> access-token
{"message":"api-<token> is not a valid configuration option"}

Rather than trying to detect secrets — a heuristic on token prefixes will rot the moment a token format changes — this checks the shape of what is about to be echoed. Configuration keys are short lowercase-hyphenated words; anything else is not a key, so there is no reason to reflect it back. The typo case that the echo exists to serve is unaffected:

$ ldcli config --set projct foo
{"message":"projct is not a valid configuration option"}     # unchanged

$ ldcli config --set api-<token> access-token
{"message":"[REDACTED] is not a valid configuration option"}  # fixed

Describe alternatives you've considered

• A --show-secrets flag. Deliberately omitted. It weakens the guarantee to "safe unless someone passes a flag", and a flag whose purpose is to print a secret tends to end up in scripts. No capability is lost without it: the config file is plain YAML at a documented path, so yq '.["access-token"]' "$XDG_CONFIG_HOME/ldcli/config.yml" still works for anyone who genuinely needs the value. Happy to add the flag if you would rather not take the behavior change unconditionally.
• Partial masking (api-••••••••cd12). Lets a human identify which token is stored, but still puts live secret characters into scrollback, and ldcli whoami already names the token without revealing it.
• A registry-driven sensitive-key set in cmd/cliflags. Attractive since AllFlagsHelp() is already the single authority for valid config keys, but promoting it from map[string]string to a struct changes a shape used by the public config --help listing, for no benefit at one sensitive key. Easy to move to later if a second one appears.

Additional context

Behavior change, so calling it out plainly: any caller parsing the token out of config --list output will now read [REDACTED]. I believe that is the point of the change rather than a regression, but it is your call whether it needs more than a patch release.

cmd/config/testdata/help.golden is unchanged — no flag is added and no description is edited.

Tests added in internal/config/config_test.go:

• Redacted() — token replaced when set; left empty when unset (asserted through json.Marshal, so omitempty is actually exercised); non-sensitive fields untouched; receiver not mutated.
• TestRedactedOutput — marshals the redacted config through output.CmdOutputSingular for both json and plaintext, asserting the token appears in neither. This is what pins sites 2 and 3 rather than just the struct.
• TestErrorDoesNotEchoNonKeyArguments — transposed --set and non-key --unset redact; a key-shaped typo still echoes verbatim.

I skipped an end-to-end config --list test on purpose: it needs viper.SetConfigFile on global state that cmd/root.go owns, and a flaky test seemed worse than a missing one. I did verify the built binary by hand in all three output modes.

Verified locally: make build, go test ./..., go vet, and golangci-lint v1.63.4 all clean; gofmt -l reports nothing in the touched files. (cmd/root.go and cmd/dev_server/projects.go are flagged by gofmt on main already — I left them alone rather than mix unrelated formatting into this diff.)