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(define-module (webid-oidc token-endpoint)
  #:use-module (webid-oidc errors)
  #:use-module (webid-oidc authorization-code)
  #:use-module (webid-oidc dpop-proof)
  #:use-module (webid-oidc jws)
  #:use-module (webid-oidc jwk)
  #:use-module (webid-oidc oidc-id-token)
  #:use-module (webid-oidc access-token)
  #:use-module ((webid-oidc stubs) #:prefix stubs:)
  #:use-module ((webid-oidc refresh-token) #:prefix refresh:)
  #:use-module (web client)
  #:use-module (web request)
  #:use-module (web response)
  #:use-module (web uri)
  #:use-module (ice-9 optargs)
  #:use-module (ice-9 receive)
  #:use-module (srfi srfi-19)
  #:use-module (rnrs bytevectors))

(define (try-handle-web-failure thunk)
  (define (error->str err)
    (if (record? err)
        (let* ((type (record-type-descriptor err))
               (get
                (lambda (slot)
                  ((record-accessor type slot) err)))
               (recurse
                (lambda (err)
                  (error->str err))))
          (case (record-type-name type)
            ((&cannot-decode-dpop-proof)
             (format #f "the DPoP proof is invalid"))
            ((&no-authorization-code)
             (format #f "there is no authorization code in the request"))
            ((&no-refresh-token)
             (format #f "there is no refresh token in the request"))
            ((&cannot-decode-authorization-code)
             (format #f "the authorization code is invalid"))
            ((&invalid-refresh-token)
             (format #f "the refresh token is invalid"))
            ((&invalid-key-for-refresh-token)
             (format #f "the refresh token is bound to another key"))
            ((&unsupported-grant-type)
             (format #f "the grant type ~s is not supported" (get 'value)))
            (else
             (raise-exception err))))
        (throw err)))
  (with-exception-handler
      (lambda (error)
        (values
         (build-response
          #:code 400
          #:reason-phrase (string-append "Bad Request: " (error->str error)))
         (error->str error)))
    thunk
    #:unwind? #t))

(define*-public (make-token-endpoint token-endpoint-uri iss alg jwk validity jti-list
                                     #:key
                                     (refresh-token-dir refresh:default-dir)
                                     (current-time current-time))
  (lambda* (request request-body)
    (try-handle-web-failure
     (lambda ()
       (when (bytevector? request-body)
         (set! request-body (utf8->string request-body)))
       (let ((current-time
              (let ((t current-time))
                (when (thunk? t)
                  (set! t (t)))
                (when (integer? t)
                  (set! t (make-time time-utc 0 t)))
                (when (time? t)
                  (set! t (time-utc->date t)))
                t))
             (form-args
              (if (and (request-content-type request)
                       (eq? (car (request-content-type request))
                            'application/x-www-form-urlencoded))
                  (filter
                   (lambda (x) x)
                   (map (lambda (kv)
                          (let ((parsed
                                 (list->vector
                                  (map (lambda (x)
                                         (uri-decode x #:decode-plus-to-space? #t))
                                       (string-split kv #\=)))))
                            (if (eq? (vector-length parsed) 2)
                                `(,(vector-ref parsed 0) . ,(vector-ref parsed 1))
                                #f)))
                        (string-split request-body #\&)))
                  '()))
             (method (request-method request))
             ;; Maybe we’re behind a reverse proxy, so the authority of
             ;; (request-uri request) is meaningless.
             (uri (build-uri (uri-scheme token-endpoint-uri)
                             #:userinfo (uri-userinfo token-endpoint-uri)
                             #:host (uri-host token-endpoint-uri)
                             #:port (uri-port token-endpoint-uri)
                             #:path (uri-path (request-uri request))
                             #:query (uri-query (request-uri request)))))
         (let ((grant-type (assoc-ref form-args "grant_type"))
               (dpop (dpop-proof-decode
                      current-time jti-list method uri
                      (assq-ref (request-headers request) 'dpop)
                      (lambda (jkt) #t))))
           (unless (and grant-type (string? grant-type))
             (raise-unsupported-grant-type #f))
           (receive (webid client-id)
               (case (string->symbol grant-type)
                 ((authorization_code)
                  (let ((code
                         (let ((str (assoc-ref form-args "code")))
                           (unless str
                             (raise-no-authorization-code))
                           (authorization-code-decode
                            current-time jti-list str jwk))))
                    (values (authorization-code-webid code)
                            (authorization-code-client-id code))))
                 ((refresh_token)
                  (let ((refresh-token (assoc-ref form-args "refresh_token")))
                    (unless refresh-token
                      (raise-no-refresh-token))
                    (refresh:with-refresh-token
                     refresh-token
                     (dpop-proof-jwk dpop)
                     values
                     #:dir refresh-token-dir)))
                 (else
                  (raise-unsupported-grant-type grant-type)))
             (let* ((iat (time-second (date->time-utc current-time)))
                    (exp (+ iat validity)))
               (let ((id-token
                      (issue-id-token
                       jwk
                       #:alg alg
                       #:webid (uri->string webid)
                       #:sub (uri->string webid)
                       #:iss (uri->string iss)
                       #:aud (uri->string client-id)
                       #:exp exp
                       #:iat iat))
                     (access-token
                      (issue-access-token
                       jwk
                       #:alg alg
                       #:webid (uri->string webid)
                       #:iss (uri->string iss)
                       #:exp exp
                       #:iat iat
                       #:client-key (dpop-proof-jwk dpop)
                       #:client-id (uri->string client-id)))
                     (refresh-token
                      (if (equal? grant-type "refresh_token")
                          (assoc-ref form-args "refresh_token")
                          (refresh:issue-refresh-token webid client-id
                                                       (jkt (dpop-proof-jwk dpop))
                                                       #:dir refresh-token-dir))))
                 (values
                  (build-response #:headers '((content-type application/json)
                                              (cache-control (no-cache no-store)))
                                  #:port #f)
                  (stubs:scm->json-string
                   `((id_token . ,id-token)
                     (access_token . ,access-token)
                     (token_type . "DPoP")
                     (expires_in . ,validity)
                     (refresh_token . ,refresh-token)))))))))))))