verae-mcp-timestamping-server-go/internal/tools/public.go

package tools

// DEC-654 (D): on the public HTTP server (mcp.verae.ai) every write needs the caller's own credential - a VeraeTime
// JWT (access_token from login) or a Verae API key - checked at api.veraetime.net - and never falls back to this
// host's stored service login. Writes that need a caller bearer: stamp (any scope), create_user, session,
// stamp_batch. Public signup is open (POST /auth/signup, no bearer) so new customers can register, then stamp
// with their own JWT. login is refused on the public server (it would replace the host credential).
// Read-only verify and hash_report stay anonymous; they may use the host login and are never rate limited (DEC-660).
//
// AI clients (Grok, Claude, Cursor) must send Authorization: Bearer on every tools/call. Grok Build:
//   bearer_token_file = "~/.verae/mcp-bearer"   # raw JWT only, not auth.properties
// or point a local stdio MCP at this binary (Public=false) so the laptop host token is used.

import (
	"context"
	"crypto/sha256"
	"errors"
	"sync"
	"time"

	"git.georgelambert.org/marchon/verae-mcp-timestamping-server-go/internal/veraetime"
	"github.com/modelcontextprotocol/go-sdk/mcp"
)

// ErrWriteNeedsKey is returned for an anonymous write on the public server.
var ErrWriteNeedsKey = errors.New(
	"this tool needs your own Verae credential on Authorization: Bearer. " +
		"Use a VeraeTime JWT (access_token from `verae login` / ~/.verae/auth.properties) " +
		"or a Verae API key from https://zap.verae.ai/portal/. " +
		"Grok Build: set mcp_servers.verae-timestamping.bearer_token_file to a file that holds only the raw token " +
		"(e.g. ~/.verae/mcp-bearer), then reconnect the MCP server; " +
		"or run this binary with -transport stdio so the laptop host login is used",
)

// ErrLoginDisabled is returned by the login tool on the public server.
var ErrLoginDisabled = errors.New(
	"login is not available on the public HTTP server (it would replace the host credential). " +
		"Sign in with `verae login` or at https://zap.verae.ai/portal/, put the JWT or API key in " +
		"Authorization: Bearer on each MCP request (Grok: bearer_token_file), " +
		"or use a local stdio MCP transport",
)

// CredentialChecker validates a caller bearer (implemented by veraetime.Client.CheckCredential).
type CredentialChecker interface {
	CheckCredential(ctx context.Context, bearer string) error
}

// writeBearer returns the caller's own validated bearer; on the public server there is no host fallback.
func (d *Deps) writeBearer(ctx context.Context, req *mcp.CallToolRequest) (string, error) {
	if !d.Public {
		return d.resolveBearer(ctx, req)
	}
	tok := BearerFromRequest(req)
	if tok == "" {
		return "", ErrWriteNeedsKey
	}
	if err := d.checkCred(ctx, tok); err != nil {
		return "", err
	}
	return tok, nil
}

// readBearer is the caller's bearer, or (anonymous, never limited - DEC-660) the host login for read-only lookups.
func (d *Deps) readBearer(ctx context.Context, req *mcp.CallToolRequest) (string, error) {
	return d.resolveBearer(ctx, req)
}

type credEntry struct {
	ok  bool
	exp time.Time
}

var (
	credMu    sync.Mutex
	credCache = map[[32]byte]credEntry{}
)

func (d *Deps) checkCred(ctx context.Context, tok string) error {
	if d.Checker == nil {
		return ErrWriteNeedsKey // fail closed
	}
	h := sha256.Sum256([]byte(tok))
	credMu.Lock()
	e, hit := credCache[h]
	credMu.Unlock()
	if hit && time.Now().Before(e.exp) {
		if e.ok {
			return nil
		}
		return errors.New("the Verae credential was not accepted")
	}
	err := d.Checker.CheckCredential(ctx, tok)
	var bad *veraetime.CredentialRejected
	if err != nil && !errors.As(err, &bad) {
		return err // upstream unavailable: not cached, fail closed
	}
	credMu.Lock()
	if len(credCache) > 10000 {
		credCache = map[[32]byte]credEntry{}
	}
	credCache[h] = credEntry{ok: err == nil, exp: time.Now().Add(60 * time.Second)}
	credMu.Unlock()
	if err != nil {
		return errors.New("the Verae credential was not accepted")
	}
	return nil
}