Make the delegation logic importable

[bajtos]

Generating a delegation requires the ucantool binary today, and the CLI takes the issuer key as a file path. A caller that holds a key in memory — a Lambda, for instance — would have to spawn a subprocess and write the private key to disk purely to satisfy an API shape.

Every cryptographic step already comes from ucantone's exported API. The only obstacle was that the orchestration lived in mkDelegation in package cmd, reading cobra flag globals. This is a move, not a rewrite.

Example Use

import "github.com/fil-forge/ucantool/pkg/ucandelegate"

res, err := ucandelegate.IssueFromPEM(pemData, ucandelegate.Request{
	Audience:       "did:key:aud",
	Commands:       []string{"/msg/send"},
	Expiration:     ucandelegate.ExpiresIn(time.Hour),
	ContainerCodec: "base64+gzip",
})
_, err = res.WriteTo(os.Stdout)

Request replaces the flag globals, and takes a Signer or PEM bytes rather than a path. Delegate and Encode are available separately for callers that want the delegations before they are encoded.

Result.WriteTo carries the rule that textual container codecs end with a newline while raw and raw+gzip are written bare, so a consumer reproduces the CLI's bytes without reimplementing the rule.

ExpiresAt and ExpiresIn exist so that setting an expiration does not require importing ucantone.

A private key leak, fixed

EncodeSignerToPEM interpolated the signer with %s. ed25519.Signer is a []byte with no String method, so the raw private key bytes rendered into the error text and from there into anything that logged it. It now formats the key DID.

(Related: fil-forge/libforge#61)

[Copilot]

Pull request overview

This PR extracts the delegation-issuing orchestration out of the CLI into an importable Go package (pkg/ucandelegate), enabling callers to issue and encode delegations directly from in-memory keys (no subprocess, no writing private keys to disk).

Changes:

• Introduces pkg/ucandelegate with Request/Result and helpers (Issue, Delegate, Encode, IssueFromPEM, ExpiresAt/ExpiresIn) to reproduce CLI delegation behavior as a library.
• Adds pkg/ucanfmt helpers for container codec defaults/parsing and textual-vs-binary detection, and reuses them from commands.
• Moves PEM-file signer loading into pkg/identity and refactors cmd/delegate to bind flags and call the library; adds tests for newline behavior and expiration semantics.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
README.md	Documents the new library usage pattern for issuing delegations without the CLI.
pkg/ucanfmt/codec.go	Adds codec parsing/defaulting and textual codec detection shared by CLI and library.
pkg/ucanfmt/codec_test.go	Tests codec parsing round-trips and textual codec classification.
pkg/ucandelegate/delegate.go	New library API for issuing/encoding delegations (extracted from CLI orchestration).
pkg/ucandelegate/delegate_test.go	Validates delegation semantics (expiration, policy, issuer/subject) and encoding/output rules.
pkg/identity/pem.go	Fixes signer formatting in errors and adds LoadSignerFromPEMFile.
pkg/identity/pem_test.go	Tests PEM file loading and missing-file error behavior.
cmd/delegate.go	Refactors CLI to build a ucandelegate.Request from flags and call the library.
cmd/delegate_test.go	Adds CLI regression tests for newline rules and codec/missing-file errors.
cmd/container/pack.go	Reuses ucanfmt codec parsing/defaults and textual detection instead of local logic.

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