
------------------------------------------------------------------
== PKCE parameters (RFC 7636)
------------------------------------------------------------------
code_verifier         1cYLvhzx4gH7jAoNyYB34Nv0jcuHMVqDPC8fFzZBuyiaYeArg2yU_LJIC2BBR8x1   (64 chars)
code_challenge        vocXBOiUBp_mSdSMvkfZUMxcKHxo021R2rZ46NndJ7c
code_challenge_method S256

The verifier never leaves the client until the token request. The challenge is
all the authorization request carries, and it is a one-way hash of the verifier.

------------------------------------------------------------------
== 1. Log in to the authorization server (browser session)
------------------------------------------------------------------
$ curl -c jar -d username=alice -d password=password -d _csrf=<token> http://localhost:9000/login
HTTP/1.1 302
Location: http://localhost:9000/

------------------------------------------------------------------
== 2. GET /oauth2/authorize  (client=demo-spa)
------------------------------------------------------------------
$ curl -b jar 'http://localhost:9000/oauth2/authorize?response_type=code&client_id=demo-spa&redirect_uri=http%3A%2F%2F127.0.0.1%3A8080%2Fauthorized&scope=openid%20orders.read&state=xyz123&code_challenge=vocXBOiUBp_mSdSMvkfZUMxcKHxo021R2rZ46NndJ7c&code_challenge_method=S256'
-> 302 http://127.0.0.1:8080/authorized?code=SEUTqNBFCouk0Ip0zD1IGctT21q8_hboy-3B5ofrsKPWUhZe43_dQ-mIhmSwgtHeHka6lyeow-SMgcVb4kLGCl0czBIt1tnbiMsJbNu3HLdW7M06FVrYILKrmJqGFsoE&state=xyz123

------------------------------------------------------------------
== 3. No consent page
------------------------------------------------------------------
The authorization endpoint went straight back to the client. Either consent is
off for this client, or every requested scope was already approved.

------------------------------------------------------------------
== 5. The authorization code
------------------------------------------------------------------
code  = SEUTqNBFCouk0Ip0zD1IGctT21q8_hboy-3B5ofrsKPWUhZe43_dQ-mIhmSwgtHeHka6lyeow-SMgcVb4kLGCl0czBIt1tnbiMsJbNu3HLdW7M06FVrYILKrmJqGFsoE
state = xyz123   (the client's own value, returned untouched - compare it)

------------------------------------------------------------------
== 6a. Exchange the code WITHOUT the verifier
------------------------------------------------------------------
This is the request an attacker who stole the code can make.
HTTP 401
(empty response body)

>>> Rejected. invalid_grant is deliberately vague: the server will not tell
>>> a caller whether the code was wrong, expired, already used, or missing a
>>> verifier, because each of those is information an attacker can use.
Note: this consumed the code. Authorization codes are single-use, so the
successful exchange below needs a fresh one.

------------------------------------------------------------------
== 6b. A fresh code, exchanged properly
------------------------------------------------------------------
fresh code = _TiGoBrAj3MPpOg3uoh76reyCg-YfoYTvHSraf-ljGyPjrPF6C0ccK_C4IG4oXjavEbTym0HttIURO7Mrt2U-YgBQ8Q_TSrgLgwpU357VYRtDm5rFdu4WVtET2Lt0YjB

$ curl -d grant_type=authorization_code -d code=... -d code_verifier=... http://localhost:9000/oauth2/token
HTTP 200
{
    "access_token": "eyJraWQiOiJmMjgxYTNkYy0zZjlmLTRkMGItOTk1YS1iZmUwYzcwYTEwODEiLCJhbGciOiJSUzI1NiJ9.eyJzdWIiOiJhbGljZSIsImF1ZCI6Im9yZGVycy1hcGkiLCJuYmYiOjE3ODc1Mzg3NTksInNjb3BlIjpbIm9wZW5pZCIsIm9yZGVycy5yZWFkIl0sInJvbGVzIjpbIkFETUlOIiwiVVNFUiJdLCJpc3MiOiJodHRwOi8vbG9jYWxob3N0OjkwMDAiLCJleHAiOjE3ODc1MzkwNTksImlhdCI6MTc4NzUzODc1OSwianRpIjoiZGYxNzJlNTgtOGMxZi00NWVlLTlkZWEtMGE3OWQ2Y2NlMDU1IiwidGVuYW50IjoiYWNtZSJ9.TGm_0gOhoVk1mSX4YVVLA6iQp_bDFTvFAjE_1DFltFyg33FLdl7tV0Z97587SB40SgL53Vx5AUan0egPVzxZscsYwUHVxQgnXHsm0FFfIGywqccXNn2IDleUAoKtMF4Lz6oMwNc9lC6XU32UgeKGOweM_IamKcHox9GnY7q9M57nG6boOp89FZzGcYsgQ9zkbG0XvzfX3WY-FS7O5cFm8oF0b3duJ3Hb3nP8WN8VrUJdOTzuGRJC9dwxZV0Ss6sI5Z-tGr0uz_Kf0tYmJ-zlx21zh6pVKHwCEnaN6T9crl4qa784DFJlW9MA4NI_E6vXOfpHbAMyRHONSrdUAcTCtA",
    "scope": "openid orders.read",
    "id_token": "eyJraWQiOiJmMjgxYTNkYy0zZjlmLTRkMGItOTk1YS1iZmUwYzcwYTEwODEiLCJhbGciOiJSUzI1NiJ9.eyJzdWIiOiJhbGljZSIsImF1ZCI6ImRlbW8tc3BhIiwiYXpwIjoiZGVtby1zcGEiLCJhdXRoX3RpbWUiOjE3ODc1Mzg3NTgsImlzcyI6Imh0dHA6Ly9sb2NhbGhvc3Q6OTAwMCIsInByZWZlcnJlZF91c2VybmFtZSI6ImFsaWNlIiwiZXhwIjoxNzg3NTQwNTU5LCJpYXQiOjE3ODc1Mzg3NTksImp0aSI6ImE5NjFkNGJkLWIwNGUtNDc1Ni04N2JkLWE5ZjI4ZjkxMWM3NCIsInNpZCI6IkNlZlExc2ZTblJkRzBMZnY0SGdhX25iZ1pPckJiWTV6dzRwN2F4U1V1ZU0ifQ.o3-P70sm-3n2GST9kQdc0TMTazGy5vjbtO6RLdkrkbqpdz5bFmEwirdZ7ajymyutPHaGF1vGpq76fnSoBCADpNtfqNJsir8aUyKoqPxGw9HLRN_Ocky3rP-XuKAVSuaplrlEiIC6CKvwoX1oH7CnJqrI1362oLaza7ThriIyzJhArrmCIZsn7AR5h0gqFp-ivMnVgPSiRI9Gg_IpD8Jr1ZREPHo6z304vpwfTU9CJeHQb2k8wWueuJJVcjnd2hfVvqqkXX9nyIqiwy3TGG_3bbEtQ4yA4uhLACcH0E1KCtFIOFPcLujcwsNa0EnsO4OLB3w1teppZyK4vpIfGUSXcA",
    "token_type": "Bearer",
    "expires_in": 299
}

------------------------------------------------------------------
== 7. The access token
------------------------------------------------------------------
{
  "alg": "RS256",
  "kid": "f281a3dc-3f9f-4d0b-995a-bfe0c70a1081"
}
{
  "aud": "orders-api",
  "exp": 1787539059,
  "iat": 1787538759,
  "iss": "http://localhost:9000",
  "jti": "df172e58-8c1f-45ee-9dea-0a79d6cce055",
  "nbf": 1787538759,
  "roles": [
    "ADMIN",
    "USER"
  ],
  "scope": [
    "openid",
    "orders.read"
  ],
  "sub": "alice",
  "tenant": "acme"
}

------------------------------------------------------------------
== 8. The id_token - a different token, for a different audience
------------------------------------------------------------------
{
  "aud": "demo-spa",
  "auth_time": 1787538758,
  "azp": "demo-spa",
  "exp": 1787540559,
  "iat": 1787538759,
  "iss": "http://localhost:9000",
  "jti": "a961d4bd-b04e-4756-87bd-a9f28f911c74",
  "preferred_username": "alice",
  "sid": "CefQ1sfSnRdG0Lfv4Hga_nbgZOrBbY5zw4p7axSUueM",
  "sub": "alice"
}

aud is the CLIENT here, not the API. Sending this to a resource server is the
classic mix-up: it verifies (same issuer, same key) and then fails the audience
check, or worse, passes it if nobody checks audience.

------------------------------------------------------------------
== 9. Calling the resource server
------------------------------------------------------------------
GET /api/orders -> 200
{"orders":[{"total":"42.00","id":1}],"subject":"alice","clientId":null,"scopes":["openid","orders.read"],"roles":["ADMIN","USER"],"tenant":"acme","audience":["orders-api"]}
GET /api/admin -> 200
{"authorities":["FactorGrantedAuthority [authority=FACTOR_BEARER, issuedAt=2026-08-24T02:32:39.220990600Z]","SCOPE_openid","ROLE_USER","SCOPE_orders.read","ROLE_ADMIN"],"message":"admin only"}

------------------------------------------------------------------
== 10. Sending the id_token instead
------------------------------------------------------------------
HTTP/1.1 401
WWW-Authenticate: Bearer error="invalid_token", error_description="An error occurred while attempting to decode the Jwt: the required audience orders-api is missing", error_uri="https://tools.ietf.org/html/rfc6750#section-3.1", resource_metadata="http://localhost:8090/.well-known/oauth-protected-resource"
