1	# OAuth 2.0 client credentials, refresh, and authorization code with PKCE over Hairpin. Source: https://github.com/paymog/bend-kit/tree/main/oauth2
2	import Base
3	import bend-kit-crypto@0.2.2.1/crypto.bend as Crypto
4	import bend-kit-hairpin@0.9.0.0/hairpin.bend as Hairpin
5	import bend-kit-http@0.36.0.0/http.bend as Http
6	import bend-kit-time@0.2.0.0/time.bend as Time
7	import bend-kit-url@0.4.1.0/url.bend as Url
8	import bend-kit-json@0.6.1.1/json.bend as Json
9	import bend-kit-encoding@0.4.0.0/encoding.bend as Enc
10	import bend-kit-bytes@0.3.2.0/bytes.bend as Bytes
11	
12	# RFC 6749 and RFC 7636. Text is a String of code points; form values go out as UTF-8.
13	# token: the token endpoint URL. secret: "" for a public client, which sends client_id in the body;
14	# a confidential client authenticates with HTTP Basic (RFC 6749 §2.3.1).
15	type Config is Data:
16	  Config{token: String, id: String, secret: String}
17	
18	# kind: token_type, as "Bearer". refresh: "" for none. scope: "" when the server did not say.
19	# expires: when the access token lapses, counted from just before the request; None without expires_in.
20	type Token is Data:
21	  Token{access: String, kind: String, refresh: String, scope: String, expires: Maybe<&2, Time.Instant>}
22	
23	# ErrNet: the request did not complete. ErrOAuth: an RFC 6749 §5.2 error with its status, or a §4.1.2.1
24	# error in a callback, status 0. ErrReply: not a Bearer token response, with its status and text. ErrState: the
25	# callback's state is not ours (§10.12). ErrCrypto: the random source or SHA-256 failed. ErrExpired: the
26	# token lapsed and has no refresh token.
27	type Err is Data:
28	  ErrNet{e: Hairpin.Err}
29	  ErrOAuth{status: U32, code: String, why: String}
30	  ErrReply{status: U32, body: String}
31	  ErrState{}
32	  ErrCrypto{code: U32, why: String}
33	  ErrExpired{}
34	
35	# ---- base64url
36	
37	def b64url.ch(+c: U32, t: String) -> String:
38	  match c:
39	    case 43:
40	      SCon{Chr{45}, t}
41	    case 47:
42	      SCon{Chr{95}, t}
43	    case 61:
44	      t
45	    case _:
46	      SCon{Chr{c}, t}
47	
48	def b64url.go(s: String) -> String:
49	  match s:
50	    case SNil{}:
51	      SNil{}
52	    case SCon{Chr{+c}, t}:
53	      b64url.ch(c, b64url.go(t))
54	
55	# Base64url without padding (RFC 4648 §5, RFC 7636 Appendix A).
56	def b64url(b: Bytes.Bytes) -> String:
57	  b64url.go(Bytes.to_base64(b))
58	
59	# ---- forms
60	
61	def utf8(+s: String) -> String:
62	  Bytes.to_string(Enc.utf8.encode(s))
63	
64	def field(m: Map<&2, String>, k: String, +v: String) -> Map<&2, String>:
65	  Map.set(&2, String, m, k, utf8(v))
66	
67	def scoped(+scope: String, +m: Map<&2, String>) -> Map<&2, String>:
68	  Bool.pick(Map<&2, String>, String.is_empty(scope), m, field(m, "scope", scope))
69	
70	def form(+k: String, +v: String) -> Map<&2, String>:
71	  field(Map.new(&2, String), k, v)
72	
73	# RFC 6749 §2.3.1: id and secret are form-encoded before base64.
74	def basic(+id: String, +secret: String) -> String:
75	  "Basic " ++ Bytes.to_base64(Bytes.from_string(Url.pct.encode_q(utf8(id)) ++ ":" ++ Url.pct.encode_q(utf8(secret))))
76	
77	def auth.headers(+id: String, +secret: String) -> Map<&2, List<&2, String>>:
78	  +h = Http.set(Http.set(Http.empty(), "content-type", "application/x-www-form-urlencoded"), "accept", "application/json")
79	  Bool.pick(Map<&2, List<&2, String>>, String.is_empty(secret), h, Http.set(h, "authorization", basic(id, secret)))
80	
81	def auth.body(+id: String, +secret: String, +m: Map<&2, String>) -> Map<&2, String>:
82	  Bool.pick(Map<&2, String>, String.is_empty(secret), field(m, "client_id", id), m)
83	
84	# The form body of a token request from cfg's client.
85	def body(+id: String, +secret: String, m: Map<&2, String>) -> String:
86	  Url.form(auth.body(id, secret, m))
87	
88	# ---- token responses (RFC 6749 §5)
89	
90	type Got is Data:
91	  Got{access: String, kind: String, refresh: String, scope: String, expires: String, error: String, desc: String}
92	
93	def got.put(g: Got, +k: String, +v: String) -> Got:
94	  Got{a, t, r, s, e, er, d} = g
95	  Got{Bool.pick(String, String.eq(k, "access_token"), v, a), Bool.pick(String, String.eq(k, "token_type"), v, t),
96	    Bool.pick(String, String.eq(k, "refresh_token"), v, r), Bool.pick(String, String.eq(k, "scope"), v, s),
97	    Bool.pick(String, String.eq(k, "expires_in"), v, e), Bool.pick(String, String.eq(k, "error"), v, er),
98	    Bool.pick(String, String.eq(k, "error_description"), v, d)}
99	
100	# A string's text, or a number's, as some servers send expires_in as "3600".
101	def got.text(v: Json.Val) -> String:
102	  match v:
103	    case Json.Str{s}:
104	      Enc.utf8.decode(s)
105	    case Json.Num{s}:
106	      Bytes.to_string(s)
107	    case other:
108	      ""
109	
110	def got.go(kvs: List<&1, Bytes.Bytes & Json.Val>, g: Got) -> Got:
111	  match kvs:
112	    case Nil{}:
113	      g
114	    case Con{(k, v), t}:
115	      got.go(t, got.put(g, Bytes.to_string(k), got.text(v)))
116	
117	def got.obj(v: Json.Val) -> Maybe<&2, Got>:
118	  match v:
119	    case Json.Obj{kvs}:
120	      Some{got.go(kvs, Got{"", "", "", "", "", "", ""})}
121	    case other:
122	      None{}
123	
124	def got(m: Maybe<&1, Json.Val>) -> Maybe<&2, Got>:
125	  match m:
126	    case None{}:
127	      None{}
128	    case Some{v}:
129	      got.obj(v)
130	
131	def expiry(now: Time.Instant, m: Maybe<&2, U32>) -> Maybe<&2, Time.Instant>:
132	  match m:
133	    case None{}:
134	      None{}
135	    case Some{n}:
136	      Some{Time.Instant.add(now, Time.Duration.of_secs(Time.i64(n)))}
137	
138	# A 2xx with an access token of type Bearer (RFC 6750 §4, case-insensitive), the only kind request sends.
139	def good(+status: U32, g: Got) -> Bool:
140	  Got{a, t, r, s, e, er, d} = g
141	  Bool.and(Bool.and(U32.is_le(200, status), U32.is_lt(status, 300)), Bool.and(Bool.not(String.is_empty(a)), String.eq(String.to_lower(t), "bearer")))
142	
143	# §6: a refresh reply without refresh_token keeps the old one. b: the body, decoded only for an error.
144	def token.pick(ok: Bool, +status: U32, +old: String, now: Time.Instant, b: Bytes.Bytes, g: Got) -> Result<&1, &1, Err, Token>:
145	  match ok:
146	    case True{}:
147	      Got{a, t, +r, s, e, er, d} = g
148	      Done{Token{a, t, Bool.pick(String, String.is_empty(r), old, r), s, expiry(now, Json.u32.num(e))}}
149	    case False{}:
150	      Got{a, t, r, s, e, +er, d} = g
151	      Fail{Bool.pick(Err, String.is_empty(er), ErrReply{status, Enc.utf8.decode(b)}, ErrOAuth{status, er, d})}
152	
153	def token.of(+status: U32, +old: String, now: Time.Instant, b: Bytes.Bytes, m: Maybe<&2, Got>) -> Result<&1, &1, Err, Token>:
154	  match m:
155	    case None{}:
156	      Fail{ErrReply{status, Enc.utf8.decode(b)}}
157	    case Some{+g}:
158	      token.pick(good(status, g), status, old, now, b, g)
159	
160	def parse.copy(+status: U32, +old: String, now: Time.Instant, r: Bytes.Bytes & Bytes.Bytes) -> Result<&1, &1, Err, Token>:
161	  (b, c) = r
162	  token.of(status, old, now, b, got(Json.parse.bytes(c)))
163	
164	# A token endpoint's reply at status, requested at now. old: the refresh token to keep when none comes back.
165	def parse(+status: U32, +old: String, now: Time.Instant, b: Bytes.Bytes) -> Result<&1, &1, Err, Token>:
166	  parse.copy(status, old, now, Bytes.slice(b, 0, 4294967295))
167	
168	def reply(+old: String, now: Time.Instant, r: Result<&1, &1, Hairpin.Err, Http.Res>) -> Result<&1, &1, Err, Token>:
169	  match r:
170	    case Fail{e}:
171	      Fail{ErrNet{e}}
172	    case Done{res}:
173	      Http.Res{+status, h, b} = res
174	      parse(status, old, now, b)
175	
176	def grant.done(+old: String, now: Time.Instant, x: Hairpin.Client & Result<&1, &1, Hairpin.Err, Http.Res>) ->
177	    Hairpin.Client & Result<&1, &1, Err, Token>:
178	  (h, r) = x
179	  (h, reply(old, now, r))
180	
181	# POST m to the token endpoint. Hairpin sends a POST once.
182	def grant(h: Hairpin.Client, cfg: Config, m: Map<&2, String>, +old: String) -> IO(Hairpin.Client & Result<&1, &1, Err, Token>):
183	  Config{url, +id, +secret} = cfg
184	  do IO<Hairpin.Client & Result<&1, &1, Err, Token>>:
185	    now : Time.Instant <- Time.now()
186	    x : Hairpin.Client & Result<&1, &1, Hairpin.Err, Http.Res> <-
187	      Hairpin.request(h, "POST", url, auth.headers(id, secret), Http.from_string(body(id, secret, m)))
188	    return grant.done(old, now, x)
189	
190	# ---- grants
191	
192	# RFC 6749 §4.4. scope: "" for the server's default.
193	def client_credentials(h: Hairpin.Client, cfg: Config, +scope: String) -> IO(Hairpin.Client & Result<&1, &1, Err, Token>):
194	  grant(h, cfg, scoped(scope, form("grant_type", "client_credentials")), "")
195	
196	# RFC 6749 §4.1.3 with RFC 7636 §4.5: the code from callback, the same redirect_uri, and the verifier.
197	def code(h: Hairpin.Client, cfg: Config, +code: String, +redirect: String, +verifier: String) ->
198	    IO(Hairpin.Client & Result<&1, &1, Err, Token>):
199	  grant(h, cfg, field(field(field(form("grant_type", "authorization_code"), "code", code), "redirect_uri", redirect), "code_verifier", verifier), "")
200	
201	def refresh.go(none: Bool, h: Hairpin.Client, cfg: Config, +r: String, +scope: String) -> IO(Hairpin.Client & Result<&1, &1, Err, Token>):
202	  match none:
203	    case True{}:
204	      IO.pure(Hairpin.Client & Result<&1, &1, Err, Token>, (h, Fail{ErrExpired{}}))
205	    case False{}:
206	      grant(h, cfg, scoped(scope, field(form("grant_type", "refresh_token"), "refresh_token", r)), r)
207	
208	# RFC 6749 §6. scope: "" keeps the granted scope. ErrExpired when tok has no refresh token.
209	def refresh(h: Hairpin.Client, cfg: Config, tok: Token, +scope: String) -> IO(Hairpin.Client & Result<&1, &1, Err, Token>):
210	  Token{a, k, +r, s, e} = tok
211	  refresh.go(String.is_empty(r), h, cfg, r, scope)
212	
213	def expiring.at(e: Maybe<&2, Time.Instant>, now: Time.Instant, +skew: U32) -> Bool:
214	  match e:
215	    case None{}:
216	      False{}
217	    case Some{at}:
218	      Bool.not(Cmp.is_lt(Time.Instant.cmp(Time.Instant.add(now, Time.Duration.of_secs(Time.i64(skew))), at)))
219	
220	# Does tok lapse within skew seconds of now? A token without expires_in never does.
221	def expiring(tok: Token, now: Time.Instant, +skew: U32) -> Bool:
222	  Token{a, k, r, s, e} = tok
223	  expiring.at(e, now, skew)
224	
225	def fresh.go(due: Bool, h: Hairpin.Client, cfg: Config, +tok: Token) -> IO(Hairpin.Client & Result<&1, &1, Err, Token>):
226	  match due:
227	    case True{}:
228	      refresh(h, cfg, tok, "")
229	    case False{}:
230	      IO.pure(Hairpin.Client & Result<&1, &1, Err, Token>, (h, Done{tok}))
231	
232	# tok, or a refreshed one when it lapses within skew seconds.
233	def fresh(h: Hairpin.Client, cfg: Config, +tok: Token, +skew: U32) -> IO(Hairpin.Client & Result<&1, &1, Err, Token>):
234	  do IO<Hairpin.Client & Result<&1, &1, Err, Token>>:
235	    now : Time.Instant <- Time.now()
236	    fresh.go(expiring(tok, now, skew), h, cfg, tok)
237	
238	def fresh.cc.go(due: Bool, h: Hairpin.Client, cfg: Config, +scope: String, +tok: Token) -> IO(Hairpin.Client & Result<&1, &1, Err, Token>):
239	  match due:
240	    case True{}:
241	      client_credentials(h, cfg, scope)
242	    case False{}:
243	      IO.pure(Hairpin.Client & Result<&1, &1, Err, Token>, (h, Done{tok}))
244	
245	# tok, or a new client-credentials token when it lapses within skew seconds (§4.4.3: no refresh token).
246	def fresh.cc(h: Hairpin.Client, cfg: Config, +scope: String, +tok: Token, +skew: U32) -> IO(Hairpin.Client & Result<&1, &1, Err, Token>):
247	  do IO<Hairpin.Client & Result<&1, &1, Err, Token>>:
248	    now : Time.Instant <- Time.now()
249	    fresh.cc.go(expiring(tok, now, skew), h, cfg, scope, tok)
250	
251	# ---- authorization code with PKCE (RFC 7636)
252	
253	def random.of(r: Result<&1, &1, U32 & String, U32 & Array<U32>>) -> Result<&1, &1, Err, String>:
254	  match r:
255	    case Fail{(c, why)}:
256	      Fail{ErrCrypto{c, why}}
257	    case Done{(len, buf)}:
258	      Done{b64url(Bytes.Bytes{len, buf})}
259	
260	# n octets from the OS secure random source, as base64url.
261	def random(+n: U32) -> IO(Result<&1, &1, Err, String>):
262	  do IO<Result<&1, &1, Err, String>>:
263	    r : Result<&1, &1, U32 & String, U32 & Array<U32>> <- Crypto.random.words(n)
264	    return random.of(r)
265	
266	# §4.1: 32 random octets, 43 unreserved chars.
267	def verifier() -> IO(Result<&1, &1, Err, String>):
268	  random(32)
269	
270	# An unguessable state for the authorization request (RFC 6749 §10.12).
271	def state() -> IO(Result<&1, &1, Err, String>):
272	  random(16)
273	
274	def challenge.words(b: Bytes.Bytes) -> IO(Result<&1, &1, Err, String>):
275	  Bytes.Bytes{+len, buf} = b
276	  do IO<Result<&1, &1, Err, String>>:
277	    r : Result<&1, &1, U32 & String, U32 & Array<U32>> <- Crypto.sha256.words(len, buf)
278	    return random.of(r)
279	
280	# §4.2 S256: BASE64URL(SHA256(ASCII(verifier))).
281	def challenge(+verifier: String) -> IO(Result<&1, &1, Err, String>):
282	  challenge.words(Bytes.from_string(verifier))
283	
284	def qmark(s: String) -> Bool:
285	  match s:
286	    case SNil{}:
287	      False{}
288	    case SCon{Chr{+c}, t}:
289	      Bool.or(U32.is_eq(c, 63), qmark(t))
290	
291	# RFC 6749 §4.1.1 with RFC 7636 §4.3: the URL to send the user to. endpoint may carry its own query.
292	def authorize.url(cfg: Config, +endpoint: String, +redirect: String, +scope: String, +state: String, +challenge: String) -> String:
293	  Config{t, +id, s} = cfg
294	  +q = field(field(field(field(field(form("response_type", "code"), "client_id", id), "redirect_uri", redirect), "state", state),
295	    "code_challenge", challenge), "code_challenge_method", "S256")
296	  endpoint ++ Bool.pick(String, qmark(endpoint), "&", "?") ++ Url.form(scoped(scope, q))
297	
298	def param.of(r: Map<&2, String> & String) -> String:
299	  (n, v) = r
300	  v
301	
302	def param(+m: Map<&2, String>, k: String) -> String:
303	  param.of(Map.get(String, "", m, k))
304	
305	def callback.pick(+err: String, desc: String, +got: String, +code: String, +state: String) -> Result<&1, &1, Err, String>:
306	  Bool.pick(Result<&1, &1, Err, String>, Bool.not(String.eq(got, state)), Fail{ErrState{}},
307	    Bool.pick(Result<&1, &1, Err, String>, Bool.not(String.is_empty(err)), Fail{ErrOAuth{0, err, desc}},
308	      Bool.pick(Result<&1, &1, Err, String>, String.is_empty(code), Fail{ErrReply{0, "no code"}}, Done{code})))
309	
310	def callback.m(+state: String, m: Maybe<&2, Url.Url>) -> Result<&1, &1, Err, String>:
311	  match m:
312	    case None{}:
313	      Fail{ErrReply{0, "bad callback query"}}
314	    case Some{Url.Url{p, +q}}:
315	      callback.pick(param(q, "error"), param(q, "error_description"), param(q, "state"), param(q, "code"), state)
316	
317	def callback.frag(+state: String, r: String & String) -> Result<&1, &1, Err, String>:
318	  (q, f) = r
319	  callback.m(state, Url.parse("/?" ++ q))
320	
321	def callback.q(+state: String, r: String & String) -> Result<&1, &1, Err, String>:
322	  (p, rest) = r
323	  callback.frag(state, Url.take_to(rest, 35))
324	
325	# §4.1.2: the code in the redirect to redirect_uri, once its state matches ours; the server's error if it sent one.
326	def callback(url: String, +state: String) -> Result<&1, &1, Err, String>:
327	  callback.q(state, Url.take_to(url, 63))
328	
329	# ---- bearer requests (RFC 6750 §2.1)
330	
331	def bearer(tok: Token, h: Map<&2, List<&2, String>>) -> Map<&2, List<&2, String>>:
332	  Token{a, k, r, s, e} = tok
333	  Http.set(h, "authorization", "Bearer " ++ a)
334	
335	# Hairpin.request with Authorization: Bearer <access>, over any authorization header in headers.
336	def request(c: Hairpin.Client, tok: Token, +method: String, url: String, headers: Map<&2, List<&2, String>>, body: Bytes.Bytes) ->
337	    IO(Hairpin.Client & Result<&1, &1, Hairpin.Err, Http.Res>):
338	  Hairpin.request(c, method, url, bearer(tok, headers), body)