{
  "issuer": "https://store.example.com",
  "authorization_endpoint": "https://store.example.com/oauth/authorize",
  "token_endpoint": "https://store.example.com/oauth/token",
  "revocation_endpoint": "https://store.example.com/oauth/revoke",
  "scopes_supported": [
    "ucp:scopes:checkout_session",
    "openid",
    "profile"
  ],
  "response_types_supported": ["code"],
  "grant_types_supported": ["authorization_code", "refresh_token"],
  "code_challenge_methods_supported": ["S256"]
}

code_verifier = 随机生成的43-128字符字符串
code_challenge = BASE64URL(SHA256(code_verifier))

GET https://store.example.com/oauth/authorize?
  response_type=code&
  client_id=agent_shopping_001&
  redirect_uri=https://agent.example.com/callback&
  scope=ucp:scopes:checkout_session&
  state=random_csrf_token_xyz&
  code_challenge=E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM&
  code_challenge_method=S256

https://agent.example.com/callback?code=auth_code_abc123&state=random_csrf_token_xyz

POST https://store.example.com/oauth/token
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&
code=auth_code_abc123&
redirect_uri=https://agent.example.com/callback&
client_id=agent_shopping_001&
client_secret=secret_xxx&
code_verifier=原始的code_verifier值

{
  "access_token": "at_ucp_xxxxxxxxxxxxx",
  "token_type": "Bearer",
  "expires_in": 3600,
  "refresh_token": "rt_ucp_xxxxxxxxxxxxx",
  "scope": "ucp:scopes:checkout_session"
}

POST https://store.example.com/oauth/revoke
Content-Type: application/x-www-form-urlencoded

token=at_ucp_xxxxxxxxxxxxx&
token_type_hint=access_token&
client_id=agent_shopping_001&
client_secret=secret_xxx

POST https://store.example.com/oauth/token
Content-Type: application/x-www-form-urlencoded

grant_type=refresh_token&
refresh_token=rt_ucp_xxxxxxxxxxxxx&
client_id=agent_shopping_001&
client_secret=secret_xxx