| 1 | // Sign in with Keymail — a hand-written client for keymail's JSON-bodied |
| 2 | // OAuth 2.1 (authorization code + PKCE S256, no client registration: |
| 3 | // client_id IS the console's origin) and its app API (sealed sends into the |
| 4 | // user's Apps inbox). |
| 5 | // |
| 6 | // Wire contract implemented from the keymail source of truth: |
| 7 | // keymail oauth.go (handleOAuthToken, handleOAuthRevoke), appapi.go |
| 8 | // (handleAppSend), federation.go (envelope), crypto.go (seal / sign / |
| 9 | // key encodings), docs/apps.md. All bodies are JSON, never form-encoded — |
| 10 | // off-the-shelf oauth2 libraries do not speak this, hence by hand. |
| 11 | package console |
| 12 | |
| 13 | import ( |
| 14 | "bytes" |
| 15 | "context" |
| 16 | "crypto/aes" |
| 17 | "crypto/cipher" |
| 18 | "crypto/ecdh" |
| 19 | "crypto/ecdsa" |
| 20 | "crypto/hkdf" |
| 21 | "crypto/rand" |
| 22 | "crypto/sha256" |
| 23 | "encoding/base64" |
| 24 | "encoding/hex" |
| 25 | "encoding/json" |
| 26 | "errors" |
| 27 | "fmt" |
| 28 | "io" |
| 29 | "net/http" |
| 30 | "net/url" |
| 31 | "strconv" |
| 32 | "strings" |
| 33 | "time" |
| 34 | ) |
| 35 | |
| 36 | // ErrGrantRevoked reports a send refused with 401: the user revoked the |
| 37 | // console's grant in Keymail (or the token is otherwise dead), so the only |
| 38 | // road back is the OAuth ceremony, which rotates the grant. |
| 39 | var ErrGrantRevoked = errors.New("keymail: grant revoked or invalid") |
| 40 | |
| 41 | // keymailError is a non-200 answer from Keymail. Error() keeps the text |
| 42 | // do() has always produced; Status and Msg let callers classify without |
| 43 | // matching strings. |
| 44 | type keymailError struct { |
| 45 | Status int |
| 46 | Method, Path string |
| 47 | Msg string // Keymail's {"error": ...}, or the HTTP status line |
| 48 | } |
| 49 | |
| 50 | func (e *keymailError) Error() string { |
| 51 | return fmt.Sprintf("keymail: %s %s: %s", e.Method, e.Path, e.Msg) |
| 52 | } |
| 53 | |
| 54 | // Keymail is a client bound to one keymail base URL and one console origin. |
| 55 | type Keymail struct { |
| 56 | base string // keymail base URL, no trailing slash |
| 57 | origin string // the console's origin — its OAuth client_id |
| 58 | signKey *ecdsa.PrivateKey |
| 59 | httpc *http.Client |
| 60 | } |
| 61 | |
| 62 | // NewKeymail builds a client. origin is the console's https origin (its |
| 63 | // client_id); baseURL the keymail deployment (https://keymail.dev). |
| 64 | func NewKeymail(baseURL, origin string) *Keymail { |
| 65 | return &Keymail{ |
| 66 | base: strings.TrimSuffix(baseURL, "/"), |
| 67 | origin: strings.TrimSuffix(origin, "/"), |
| 68 | httpc: &http.Client{Timeout: 15 * time.Second}, |
| 69 | } |
| 70 | } |
| 71 | |
| 72 | // Host is the hostname of the configured Keymail deployment (keymail.dev for |
| 73 | // https://keymail.dev), lowercased, no port. An address at this host is a |
| 74 | // Keymail address whatever a lookup says. |
| 75 | func (k *Keymail) Host() string { |
| 76 | u, err := url.Parse(k.base) |
| 77 | if err != nil { |
| 78 | return "" |
| 79 | } |
| 80 | return strings.ToLower(u.Hostname()) |
| 81 | } |
| 82 | |
| 83 | // SetSigningKey installs the console's long-lived envelope-signing key |
| 84 | // (ECDSA P-256). With a key set the client asks for scope "identify send" |
| 85 | // and pins the key into the grant at exchange (keymail requires sign_pub |
| 86 | // whenever the grant can deliver mail); without one it asks for bare |
| 87 | // "identify" and cannot SendApp. |
| 88 | func (k *Keymail) SetSigningKey(priv *ecdsa.PrivateKey) { k.signKey = priv } |
| 89 | |
| 90 | // SignPub is the base64 raw uncompressed P-256 point keymail pins in the |
| 91 | // grant ("" when no key is set). |
| 92 | func (k *Keymail) SignPub() string { |
| 93 | if k.signKey == nil { |
| 94 | return "" |
| 95 | } |
| 96 | pub, err := k.signKey.PublicKey.ECDH() |
| 97 | if err != nil { |
| 98 | return "" |
| 99 | } |
| 100 | return base64.StdEncoding.EncodeToString(pub.Bytes()) |
| 101 | } |
| 102 | |
| 103 | func (k *Keymail) scope() string { |
| 104 | if k.signKey != nil { |
| 105 | return "identify send" |
| 106 | } |
| 107 | return "identify" |
| 108 | } |
| 109 | |
| 110 | // redirectURI is fixed by the console's route table. |
| 111 | func (k *Keymail) redirectURI() string { return k.origin + "/auth/callback" } |
| 112 | |
| 113 | // stepUpRedirectURI is where a re-authentication lands. A separate route from |
| 114 | // the sign-in callback on purpose: a code minted for a step-up must not be |
| 115 | // spendable as a sign-in, and a sign-in must never be able to satisfy a |
| 116 | // step-up — the two flows never share a landing pad or a state cookie. |
| 117 | func (k *Keymail) stepUpRedirectURI() string { return k.origin + "/auth/stepup/callback" } |
| 118 | |
| 119 | // AuthorizeURL is where the browser goes to approve the console. |
| 120 | func (k *Keymail) AuthorizeURL(state, challenge string) string { |
| 121 | return k.authorizeURL(state, challenge, k.redirectURI(), 0) |
| 122 | } |
| 123 | |
| 124 | // StepUpURL is the same ceremony with one extra demand: a FRESH authenticator |
| 125 | // gesture, however live the user's Keymail session is. `prompt=login` is the |
| 126 | // ask; `max_age` is the same ask spelled for an IdP that only understands |
| 127 | // seconds, and both are sent because the tighter of the two wins at Keymail. |
| 128 | // The redirect lands on the step-up callback, not the sign-in one — a step-up |
| 129 | // must never be mistakable for a sign-in, in either direction. |
| 130 | func (k *Keymail) StepUpURL(state, challenge string, window time.Duration) string { |
| 131 | return k.authorizeURL(state, challenge, k.stepUpRedirectURI(), window) |
| 132 | } |
| 133 | |
| 134 | func (k *Keymail) authorizeURL(state, challenge, redirect string, window time.Duration) string { |
| 135 | q := url.Values{ |
| 136 | "client_id": {k.origin}, |
| 137 | "redirect_uri": {redirect}, |
| 138 | "scope": {k.scope()}, |
| 139 | "state": {state}, |
| 140 | "code_challenge": {challenge}, |
| 141 | "code_challenge_method": {"S256"}, |
| 142 | } |
| 143 | if window > 0 { |
| 144 | q.Set("prompt", "login") |
| 145 | q.Set("max_age", strconv.Itoa(int(window.Seconds()))) |
| 146 | } |
| 147 | return k.base + "/oauth/authorize?" + q.Encode() |
| 148 | } |
| 149 | |
| 150 | // SupportsStepUp asks the deployment whether it can re-authenticate anyone at |
| 151 | // all: `/.well-known/keymail` advertises `reauth` where step-up exists (only |
| 152 | // the relay shape has an identity service behind it). An error here is NOT a |
| 153 | // "probably yes" — callers must treat both a false and an error as "cannot", |
| 154 | // because the alternative is walking a human through a ceremony that was never |
| 155 | // going to produce proof and then deciding what to do about it afterwards. |
| 156 | func (k *Keymail) SupportsStepUp(ctx context.Context) (bool, error) { |
| 157 | var out struct { |
| 158 | Reauth bool `json:"reauth"` |
| 159 | } |
| 160 | if _, err := k.do(ctx, http.MethodGet, "/.well-known/keymail", "", nil, &out); err != nil { |
| 161 | return false, err |
| 162 | } |
| 163 | return out.Reauth, nil |
| 164 | } |
| 165 | |
| 166 | // Grant is one completed ceremony: who the user is, the console's access |
| 167 | // token, and — for a step-up — when the authenticator gesture behind it |
| 168 | // happened. |
| 169 | type Grant struct { |
| 170 | Address string |
| 171 | Token string |
| 172 | // AuthTime is zero when Keymail proved no gesture. Zero is the only honest |
| 173 | // representation of "it did not say", and the caller MUST treat it as a |
| 174 | // refusal rather than substituting now: a fabricated freshness is worse |
| 175 | // than no freshness, because it looks like proof. |
| 176 | AuthTime time.Time |
| 177 | } |
| 178 | |
| 179 | // Exchange trades the callback's code (plus the PKCE verifier) for the |
| 180 | // user's address and the console's access token, server-side. |
| 181 | func (k *Keymail) Exchange(ctx context.Context, code, verifier string) (address, token string, err error) { |
| 182 | g, err := k.ExchangeGrant(ctx, code, verifier, false) |
| 183 | return g.Address, g.Token, err |
| 184 | } |
| 185 | |
| 186 | // ExchangeGrant is Exchange with the step-up answer attached. stepUp selects |
| 187 | // which redirect_uri is replayed — Keymail re-checks it against the one the |
| 188 | // authorization was minted for, so a code from the sign-in flow cannot be |
| 189 | // spent here and vice versa. |
| 190 | func (k *Keymail) ExchangeGrant(ctx context.Context, code, verifier string, stepUp bool) (Grant, error) { |
| 191 | redirect := k.redirectURI() |
| 192 | if stepUp { |
| 193 | redirect = k.stepUpRedirectURI() |
| 194 | } |
| 195 | req := map[string]string{ |
| 196 | "code": code, |
| 197 | "code_verifier": verifier, |
| 198 | "client_id": k.origin, |
| 199 | "redirect_uri": redirect, |
| 200 | } |
| 201 | if sp := k.SignPub(); sp != "" { |
| 202 | req["sign_pub"] = sp |
| 203 | } |
| 204 | var out struct { |
| 205 | AccessToken string `json:"access_token"` |
| 206 | TokenType string `json:"token_type"` |
| 207 | Scope string `json:"scope"` |
| 208 | Address string `json:"address"` |
| 209 | AuthTime int64 `json:"auth_time"` |
| 210 | } |
| 211 | if _, err := k.do(ctx, http.MethodPost, "/api/oauth/token", "", req, &out); err != nil { |
| 212 | return Grant{}, err |
| 213 | } |
| 214 | if !strings.EqualFold(out.TokenType, "bearer") { |
| 215 | return Grant{}, fmt.Errorf("keymail: token exchange returned token_type %q, want bearer", out.TokenType) |
| 216 | } |
| 217 | if out.AccessToken == "" || out.Address == "" { |
| 218 | return Grant{}, errors.New("keymail: token exchange returned an empty token or address") |
| 219 | } |
| 220 | g := Grant{Address: out.Address, Token: out.AccessToken} |
| 221 | if out.AuthTime > 0 { |
| 222 | g.AuthTime = time.Unix(out.AuthTime, 0) |
| 223 | } |
| 224 | return g, nil |
| 225 | } |
| 226 | |
| 227 | // Revoke retires an access token (RFC 7009 manners server-side: always 200, |
| 228 | // revealing nothing). Callers treat failures as best-effort. |
| 229 | func (k *Keymail) Revoke(ctx context.Context, token string) error { |
| 230 | _, err := k.do(ctx, http.MethodPost, "/api/oauth/revoke", "", map[string]string{"token": token}, nil) |
| 231 | return err |
| 232 | } |
| 233 | |
| 234 | // ---- app send (the returning-sign-in confirmation channel) ------------------ |
| 235 | |
| 236 | // envelope is keymail's message-in-flight shape (federation.go): plaintext |
| 237 | // routing headers, subject+body sealed to the recipient's box key in blob, |
| 238 | // sig the sender's ECDSA signature over headers+blob. |
| 239 | type envelope struct { |
| 240 | V string `json:"v"` |
| 241 | ID string `json:"id"` |
| 242 | From string `json:"from"` |
| 243 | To string `json:"to"` |
| 244 | Date string `json:"date"` |
| 245 | SignPub string `json:"sign_pub"` |
| 246 | Blob string `json:"blob"` |
| 247 | Sig string `json:"sig"` |
| 248 | } |
| 249 | |
| 250 | const ( |
| 251 | protocolVersion = "keymail1" |
| 252 | envelopeInfo = "keymail-envelope-v1" |
| 253 | envSigContext = "keymail-env-v1" |
| 254 | ) |
| 255 | |
| 256 | // sealEnvelope seals {subject, body} to the recipient's box key and signs |
| 257 | // the envelope with the console's key. SendApp and SendFederated share it, |
| 258 | // so the two wires cannot drift apart. |
| 259 | func (k *Keymail) sealEnvelope(from, to, boxPub, subject, body string) (envelope, error) { |
| 260 | payload, err := json.Marshal(map[string]string{"subject": subject, "body": body}) |
| 261 | if err != nil { |
| 262 | return envelope{}, err |
| 263 | } |
| 264 | blob, err := sealToBox(boxPub, payload) |
| 265 | if err != nil { |
| 266 | return envelope{}, fmt.Errorf("keymail: seal to %s: %w", to, err) |
| 267 | } |
| 268 | idb := make([]byte, 16) |
| 269 | if _, err := rand.Read(idb); err != nil { |
| 270 | return envelope{}, err |
| 271 | } |
| 272 | id := hex.EncodeToString(idb) |
| 273 | date := time.Now().UTC().Format(time.RFC3339) |
| 274 | sig, err := signRaw(k.signKey, envelopeMsg(id, from, to, date, blob)) |
| 275 | if err != nil { |
| 276 | return envelope{}, err |
| 277 | } |
| 278 | return envelope{ |
| 279 | V: protocolVersion, ID: id, From: from, To: to, Date: date, |
| 280 | SignPub: k.SignPub(), Blob: blob, Sig: sig, |
| 281 | }, nil |
| 282 | } |
| 283 | |
| 284 | // SendApp delivers one sealed message (kind "app" → the user's Apps inbox) |
| 285 | // to the granting user, using the stored grant token. It looks up the |
| 286 | // recipient's box key, seals {subject, body} to it, signs the envelope with |
| 287 | // the console's pinned key, and posts it. Returns the envelope id (the |
| 288 | // sender mints it, so a deep link is knowable up front). A 401 comes back |
| 289 | // as ErrGrantRevoked. |
| 290 | func (k *Keymail) SendApp(ctx context.Context, token, to, subject, body string) (msgID string, err error) { |
| 291 | if k.signKey == nil { |
| 292 | return "", errors.New("keymail: SendApp requires a signing key") |
| 293 | } |
| 294 | // From is pinned server-side to the console's own origin host — the |
| 295 | // console writes as itself, never as anyone the user might trust. |
| 296 | from := "console@" + OriginHost(k.origin) |
| 297 | var lr struct { |
| 298 | BoxPub string `json:"box_pub"` |
| 299 | } |
| 300 | lu := "/api/federation/lookup?addr=" + url.QueryEscape(to) + "&from=" + url.QueryEscape(from) |
| 301 | if _, err := k.do(ctx, http.MethodGet, lu, "", nil, &lr); err != nil { |
| 302 | return "", fmt.Errorf("keymail: lookup %s: %w", to, err) |
| 303 | } |
| 304 | env, err := k.sealEnvelope(from, to, lr.BoxPub, subject, body) |
| 305 | if err != nil { |
| 306 | return "", err |
| 307 | } |
| 308 | status, err := k.do(ctx, http.MethodPost, "/api/app/send", token, |
| 309 | map[string]any{"envelope": env, "kind": "app"}, nil) |
| 310 | if status == http.StatusUnauthorized { |
| 311 | return "", ErrGrantRevoked |
| 312 | } |
| 313 | if err != nil { |
| 314 | return "", err |
| 315 | } |
| 316 | return env.ID, nil |
| 317 | } |
| 318 | |
| 319 | // OriginHost strips the scheme off an origin: the host (with port, if any) |
| 320 | // that keymail treats as the app's identity. |
| 321 | func OriginHost(origin string) string { |
| 322 | h := strings.TrimPrefix(origin, "https://") |
| 323 | return strings.TrimPrefix(h, "http://") |
| 324 | } |
| 325 | |
| 326 | // ---- HTTP plumbing ---------------------------------------------------------- |
| 327 | |
| 328 | // do runs one JSON round-trip. Non-200 answers become an error carrying the |
| 329 | // server's {"error": ...} text; the status is returned either way so callers |
| 330 | // can classify (401 → revoked grant). |
| 331 | func (k *Keymail) do(ctx context.Context, method, path, bearer string, in, out any) (int, error) { |
| 332 | var body io.Reader |
| 333 | if in != nil { |
| 334 | raw, err := json.Marshal(in) |
| 335 | if err != nil { |
| 336 | return 0, err |
| 337 | } |
| 338 | body = bytes.NewReader(raw) |
| 339 | } |
| 340 | req, err := http.NewRequestWithContext(ctx, method, k.base+path, body) |
| 341 | if err != nil { |
| 342 | return 0, err |
| 343 | } |
| 344 | if in != nil { |
| 345 | req.Header.Set("Content-Type", "application/json") |
| 346 | } |
| 347 | if bearer != "" { |
| 348 | req.Header.Set("Authorization", "Bearer "+bearer) |
| 349 | } |
| 350 | res, err := k.httpc.Do(req) |
| 351 | if err != nil { |
| 352 | return 0, err |
| 353 | } |
| 354 | defer res.Body.Close() |
| 355 | raw, err := io.ReadAll(io.LimitReader(res.Body, 1<<20)) |
| 356 | if err != nil { |
| 357 | return res.StatusCode, err |
| 358 | } |
| 359 | if res.StatusCode != http.StatusOK { |
| 360 | var e struct { |
| 361 | Error string `json:"error"` |
| 362 | } |
| 363 | msg := res.Status |
| 364 | if json.Unmarshal(raw, &e) == nil && e.Error != "" { |
| 365 | msg = e.Error |
| 366 | } |
| 367 | return res.StatusCode, &keymailError{Status: res.StatusCode, Method: method, Path: path, Msg: msg} |
| 368 | } |
| 369 | if out != nil { |
| 370 | if err := json.Unmarshal(raw, out); err != nil { |
| 371 | return res.StatusCode, fmt.Errorf("keymail: %s %s: bad response body: %v", method, path, err) |
| 372 | } |
| 373 | } |
| 374 | return res.StatusCode, nil |
| 375 | } |
| 376 | |
| 377 | // ---- PKCE ------------------------------------------------------------------- |
| 378 | |
| 379 | // NewVerifier mints a PKCE code verifier (43 base64url chars — inside the |
| 380 | // RFC 7636 window). Also serves as the state generator. |
| 381 | func NewVerifier() (string, error) { |
| 382 | b := make([]byte, 32) |
| 383 | if _, err := rand.Read(b); err != nil { |
| 384 | return "", err |
| 385 | } |
| 386 | return base64.RawURLEncoding.EncodeToString(b), nil |
| 387 | } |
| 388 | |
| 389 | // ChallengeS256 derives the S256 code challenge for a verifier. |
| 390 | func ChallengeS256(verifier string) string { |
| 391 | sum := sha256.Sum256([]byte(verifier)) |
| 392 | return base64.RawURLEncoding.EncodeToString(sum[:]) |
| 393 | } |
| 394 | |
| 395 | // ---- envelope crypto (ported from keymail crypto.go, byte-compatible) ------- |
| 396 | |
| 397 | // envelopeMsg is what a sender signs per message: routing headers and the |
| 398 | // ciphertext, so tampering with any of them breaks the signature. |
| 399 | func envelopeMsg(id, from, to, date, blob string) []byte { |
| 400 | return []byte(envSigContext + "\n" + id + "\n" + from + "\n" + to + "\n" + date + "\n" + blob) |
| 401 | } |
| 402 | |
| 403 | // signRaw produces a WebCrypto-compatible raw r||s ECDSA P-256 signature. |
| 404 | func signRaw(priv *ecdsa.PrivateKey, msg []byte) (string, error) { |
| 405 | h := sha256.Sum256(msg) |
| 406 | r, s, err := ecdsa.Sign(rand.Reader, priv, h[:]) |
| 407 | if err != nil { |
| 408 | return "", err |
| 409 | } |
| 410 | sig := make([]byte, 64) |
| 411 | r.FillBytes(sig[:32]) |
| 412 | s.FillBytes(sig[32:]) |
| 413 | return base64.StdEncoding.EncodeToString(sig), nil |
| 414 | } |
| 415 | |
| 416 | // sealToBox encrypts payload to a recipient box key: ephemeral ECDH P-256 → |
| 417 | // HKDF-SHA256("keymail-envelope-v1") → AES-GCM-256, blob = ephPub(65) || |
| 418 | // iv(12) || ciphertext, base64 (std). |
| 419 | func sealToBox(recipientBoxPubB64 string, payload []byte) (string, error) { |
| 420 | raw, err := base64.StdEncoding.DecodeString(recipientBoxPubB64) |
| 421 | if err != nil { |
| 422 | return "", errors.New("bad recipient key encoding") |
| 423 | } |
| 424 | pub, err := ecdh.P256().NewPublicKey(raw) |
| 425 | if err != nil { |
| 426 | return "", fmt.Errorf("bad recipient key: %w", err) |
| 427 | } |
| 428 | eph, err := ecdh.P256().GenerateKey(rand.Reader) |
| 429 | if err != nil { |
| 430 | return "", err |
| 431 | } |
| 432 | shared, err := eph.ECDH(pub) |
| 433 | if err != nil { |
| 434 | return "", err |
| 435 | } |
| 436 | key, err := hkdf.Key(sha256.New, shared, nil, envelopeInfo, 32) |
| 437 | if err != nil { |
| 438 | return "", err |
| 439 | } |
| 440 | block, err := aes.NewCipher(key) |
| 441 | if err != nil { |
| 442 | return "", err |
| 443 | } |
| 444 | gcm, err := cipher.NewGCM(block) |
| 445 | if err != nil { |
| 446 | return "", err |
| 447 | } |
| 448 | iv := make([]byte, 12) |
| 449 | if _, err := rand.Read(iv); err != nil { |
| 450 | return "", err |
| 451 | } |
| 452 | ct := gcm.Seal(nil, iv, payload, nil) |
| 453 | blob := append(append(eph.PublicKey().Bytes(), iv...), ct...) |
| 454 | return base64.StdEncoding.EncodeToString(blob), nil |
| 455 | } |
| 456 | |
amadan