fluid-telegram/internal/secrets/secrets.go

// Package secrets is the provisioner's only route to credentials.
//
// Everything sensitive lives in OpenBao: the operator's MTProto session, the
// app credentials, the bot token, and the redaction salt. Nothing here writes a
// secret to disk, and nothing returns one in an error message -- an error says
// which path failed, never what was at it.
package secrets

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	"strings"
	"time"
)

// Paths under the interface's subtree. The campaign is part of the path so that
// two campaigns on one interface cannot read each other's credentials.
const (
	KeyOperatorApp     = "operator-app"     // api_id, api_hash
	KeyOperatorSession = "operator-session" // MTProto session; a full-account credential
	KeyBotToken        = "bot-token"
	KeyRedactionSalt   = "redaction-salt"
)

type Store struct {
	addr   string
	token  string
	mount  string
	prefix string
	hc     *http.Client
}

// NewFromEnv builds a store from the ambient OpenBao configuration.
func NewFromEnv(campaign string) (*Store, error) {
	addr := firstNonEmpty(os.Getenv("BAO_ADDR"), os.Getenv("VAULT_ADDR"))
	token := firstNonEmpty(os.Getenv("BAO_TOKEN"), os.Getenv("VAULT_TOKEN"))
	// Name the variable that is actually missing. "set both" sends someone
	// checking the one they already set.
	switch {
	case addr == "" && token == "":
		return nil, fmt.Errorf("OpenBao is not configured: set BAO_ADDR and BAO_TOKEN " +
			"(see docs/seeding-runbook.md)")
	case addr == "":
		return nil, fmt.Errorf("BAO_ADDR is not set (BAO_TOKEN is)")
	case token == "":
		return nil, fmt.Errorf("BAO_TOKEN is not set (BAO_ADDR is %s)", addr)
	}
	mount := firstNonEmpty(os.Getenv("BAO_MOUNT"), "secret")
	return &Store{
		addr:   strings.TrimSuffix(addr, "/"),
		token:  token,
		mount:  mount,
		prefix: "fluid-telegram/" + campaign + "/telegram",
		hc:     &http.Client{Timeout: 20 * time.Second},
	}, nil
}

func (s *Store) path(key string) string {
	return fmt.Sprintf("%s/v1/%s/data/%s/%s", s.addr, s.mount, s.prefix, key)
}

// Ref is the human-readable location of a secret, safe to print. Used in plans
// and error messages so an operator can find what is missing.
func (s *Store) Ref(key string) string {
	return fmt.Sprintf("bao:%s/%s/%s", s.mount, s.prefix, key)
}

type kvPayload struct {
	Data struct {
		Data map[string]string `json:"data"`
	} `json:"data"`
}

// Get returns the fields at a path. Missing is reported as (nil, false, nil):
// absence is an ordinary state on a first run, not a failure.
func (s *Store) Get(ctx context.Context, key string) (map[string]string, bool, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, s.path(key), nil)
	if err != nil {
		return nil, false, err
	}
	req.Header.Set("X-Vault-Token", s.token)
	resp, err := s.hc.Do(req)
	if err != nil {
		return nil, false, fmt.Errorf("read %s: %w", s.Ref(key), err)
	}
	defer resp.Body.Close()

	switch resp.StatusCode {
	case http.StatusNotFound:
		return nil, false, nil
	case http.StatusOK:
	default:
		return nil, false, fmt.Errorf("read %s: unexpected status %s", s.Ref(key), resp.Status)
	}
	var p kvPayload
	if err := json.NewDecoder(resp.Body).Decode(&p); err != nil {
		return nil, false, fmt.Errorf("read %s: %w", s.Ref(key), err)
	}
	return p.Data.Data, true, nil
}

// Put replaces the fields at a path.
func (s *Store) Put(ctx context.Context, key string, fields map[string]string) error {
	body, err := json.Marshal(map[string]any{"data": fields})
	if err != nil {
		return err
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, s.path(key), bytes.NewReader(body))
	if err != nil {
		return err
	}
	req.Header.Set("X-Vault-Token", s.token)
	req.Header.Set("Content-Type", "application/json")
	resp, err := s.hc.Do(req)
	if err != nil {
		return fmt.Errorf("write %s: %w", s.Ref(key), err)
	}
	defer resp.Body.Close()
	if resp.StatusCode >= 300 {
		return fmt.Errorf("write %s: unexpected status %s", s.Ref(key), resp.Status)
	}
	return nil
}

// CreateIfAbsent writes fields only when nothing is there, and reports whether
// it wrote. It has no counterpart that overwrites, and that is deliberate: the
// redaction salt is stored this way, and rotating it silently invalidates every
// longitudinal comparison the interface has made, with no visible failure. A
// tool that can rewrite it is a tool that eventually will.
func (s *Store) CreateIfAbsent(ctx context.Context, key string, fields map[string]string) (bool, error) {
	_, found, err := s.Get(ctx, key)
	if err != nil {
		return false, err
	}
	if found {
		return false, nil
	}
	return true, s.Put(ctx, key, fields)
}

func firstNonEmpty(vals ...string) string {
	for _, v := range vals {
		if v != "" {
			return v
		}
	}
	return ""
}