/*
This file is part of GNUnet
Copyright (C) 2010-2015 GNUnet e.V.
GNUnet is free software: you can redistribute it and/or modify it
under the terms of the GNU Affero General Public License as published
by the Free Software Foundation, either version 3 of the License,
or (at your option) any later version.
GNUnet is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see .
SPDX-License-Identifier: AGPL3.0-or-later
*/
/**
* @file reclaim/oidc_helper.c
* @brief helper library for OIDC related functions
* @author Martin Schanzenbach
*/
#include "platform.h"
#include
#include
#include "gnunet_util_lib.h"
#include "gnunet_reclaim_attribute_lib.h"
#include "gnunet_reclaim_service.h"
#include "gnunet_signatures.h"
#include "oidc_helper.h"
// #include "benchmark.h"
#include
GNUNET_NETWORK_STRUCT_BEGIN
/**
* The signature used to generate the authorization code
*/
struct OIDC_Parameters
{
/**
* The reclaim ticket
*/
struct GNUNET_RECLAIM_Ticket ticket;
/**
* The nonce
*/
uint32_t nonce GNUNET_PACKED;
/**
* The length of the PKCE code_challenge
*/
uint32_t code_challenge_len GNUNET_PACKED;
/**
* The length of the attributes list
*/
uint32_t attr_list_len GNUNET_PACKED;
};
GNUNET_NETWORK_STRUCT_END
static char *
create_jwt_header (void)
{
json_t *root;
char *json_str;
root = json_object ();
json_object_set_new (root, JWT_ALG, json_string (JWT_ALG_VALUE));
json_object_set_new (root, JWT_TYP, json_string (JWT_TYP_VALUE));
json_str = json_dumps (root, JSON_INDENT (0) | JSON_COMPACT);
json_decref (root);
return json_str;
}
static void
replace_char (char *str, char find, char replace)
{
char *current_pos = strchr (str, find);
while (current_pos)
{
*current_pos = replace;
current_pos = strchr (current_pos, find);
}
}
// RFC4648
static void
fix_base64 (char *str)
{
// Replace + with -
replace_char (str, '+', '-');
// Replace / with _
replace_char (str, '/', '_');
}
/**
* Create a JWT from attributes
*
* @param aud_key the public of the audience
* @param sub_key the public key of the subject
* @param attrs the attribute list
* @param expiration_time the validity of the token
* @param secret_key the key used to sign the JWT
* @return a new base64-encoded JWT string.
*/
char *
OIDC_id_token_new (const struct GNUNET_CRYPTO_EcdsaPublicKey *aud_key,
const struct GNUNET_CRYPTO_EcdsaPublicKey *sub_key,
const struct GNUNET_RECLAIM_ATTRIBUTE_ClaimList *attrs,
const struct GNUNET_TIME_Relative *expiration_time,
const char *nonce,
const char *secret_key)
{
struct GNUNET_RECLAIM_ATTRIBUTE_ClaimListEntry *le;
struct GNUNET_HashCode signature;
struct GNUNET_TIME_Absolute exp_time;
struct GNUNET_TIME_Absolute time_now;
char *audience;
char *subject;
char *header;
char *body_str;
char *result;
char *header_base64;
char *body_base64;
char *signature_target;
char *signature_base64;
char *attr_val_str;
json_t *body;
// iat REQUIRED time now
time_now = GNUNET_TIME_absolute_get ();
// exp REQUIRED time expired from config
exp_time = GNUNET_TIME_absolute_add (time_now, *expiration_time);
// auth_time only if max_age
// nonce only if nonce
// OPTIONAL acr,amr,azp
subject =
GNUNET_STRINGS_data_to_string_alloc (sub_key,
sizeof(struct
GNUNET_CRYPTO_EcdsaPublicKey));
audience =
GNUNET_STRINGS_data_to_string_alloc (aud_key,
sizeof(struct
GNUNET_CRYPTO_EcdsaPublicKey));
header = create_jwt_header ();
body = json_object ();
// iss REQUIRED case sensitive server uri with https
// The issuer is the local reclaim instance (e.g.
// https://reclaim.id/api/openid)
json_object_set_new (body, "iss", json_string (SERVER_ADDRESS));
// sub REQUIRED public key identity, not exceed 255 ASCII length
json_object_set_new (body, "sub", json_string (subject));
// aud REQUIRED public key client_id must be there
json_object_set_new (body, "aud", json_string (audience));
// iat
json_object_set_new (body,
"iat",
json_integer (time_now.abs_value_us / (1000 * 1000)));
// exp
json_object_set_new (body,
"exp",
json_integer (exp_time.abs_value_us / (1000 * 1000)));
// nbf
json_object_set_new (body,
"nbf",
json_integer (time_now.abs_value_us / (1000 * 1000)));
// nonce
if (NULL != nonce)
json_object_set_new (body, "nonce", json_string (nonce));
for (le = attrs->list_head; NULL != le; le = le->next)
{
attr_val_str =
GNUNET_RECLAIM_ATTRIBUTE_value_to_string (le->claim->type,
le->claim->data,
le->claim->data_size);
json_object_set_new (body, le->claim->name, json_string (attr_val_str));
GNUNET_free (attr_val_str);
}
body_str = json_dumps (body, JSON_INDENT (0) | JSON_COMPACT);
json_decref (body);
GNUNET_STRINGS_base64_encode (header, strlen (header), &header_base64);
fix_base64 (header_base64);
GNUNET_STRINGS_base64_encode (body_str, strlen (body_str), &body_base64);
fix_base64 (body_base64);
GNUNET_free (subject);
GNUNET_free (audience);
/**
* Creating the JWT signature. This might not be
* standards compliant, check.
*/
GNUNET_asprintf (&signature_target, "%s.%s", header_base64, body_base64);
GNUNET_CRYPTO_hmac_raw (secret_key,
strlen (secret_key),
signature_target,
strlen (signature_target),
&signature);
GNUNET_STRINGS_base64_encode ((const char *) &signature,
sizeof(struct GNUNET_HashCode),
&signature_base64);
fix_base64 (signature_base64);
GNUNET_asprintf (&result,
"%s.%s.%s",
header_base64,
body_base64,
signature_base64);
GNUNET_free (signature_target);
GNUNET_free (header);
GNUNET_free (body_str);
GNUNET_free (signature_base64);
GNUNET_free (body_base64);
GNUNET_free (header_base64);
return result;
}
/* Converts a hex character to its integer value */
static char
from_hex (char ch)
{
return isdigit (ch) ? ch - '0' : tolower (ch) - 'a' + 10;
}
/* Converts an integer value to its hex character*/
static char
to_hex (char code)
{
static char hex[] = "0123456789abcdef";
return hex[code & 15];
}
/* Returns a url-encoded version of str */
/* IMPORTANT: be sure to free() the returned string after use */
static char *
url_encode (const char *str)
{
char *pstr = (char *) str;
char *buf = GNUNET_malloc (strlen (str) * 3 + 1);
char *pbuf = buf;
while (*pstr)
{
if (isalnum (*pstr) || (*pstr == '-') || (*pstr == '_') || (*pstr == '.') ||
(*pstr == '~') )
*pbuf++ = *pstr;
else if (*pstr == ' ')
*pbuf++ = '+';
else
{
*pbuf++ = '%';
*pbuf++ = to_hex (*pstr >> 4);
*pbuf++ = to_hex (*pstr & 15);
}
pstr++;
}
*pbuf = '\0';
return buf;
}
/* Returns a url-decoded version of str */
/* IMPORTANT: be sure to free() the returned string after use */
static char *
url_decode (const char *str)
{
char *pstr = (char *) str;
char *buf = GNUNET_malloc (strlen (str) + 1);
char *pbuf = buf;
while (*pstr)
{
if (*pstr == '%')
{
if (pstr[1] && pstr[2])
{
*pbuf++ = from_hex (pstr[1]) << 4 | from_hex (pstr[2]);
pstr += 2;
}
}
else if (*pstr == '+')
{
*pbuf++ = ' ';
}
else
{
*pbuf++ = *pstr;
}
pstr++;
}
*pbuf = '\0';
return buf;
}
/**
* Returns base64 encoded string urlencoded
*
* @param string the string to encode
* @return base64 encoded string
*/
static char *
base64_and_urlencode (const char *data, size_t data_size)
{
char *enc;
char *urlenc;
GNUNET_STRINGS_base64_encode (data, data_size, &enc);
urlenc = url_encode (enc);
GNUNET_free (enc);
return urlenc;
}
/**
* Returns base64 encoded string urlencoded
*
* @param string the string to encode
* @return base64 encoded string
*/
static char *
base64url_encode (const char *data, size_t data_size)
{
char *enc;
size_t pos;
GNUNET_STRINGS_base64_encode (data, data_size, &enc);
// Replace with correct characters for base64url
pos = 0;
while ('\0' != enc[pos])
{
if ('+' == enc[pos])
enc[pos] = '-';
if ('/' == enc[pos])
enc[pos] = '_';
if ('=' == enc[pos])
{
enc[pos] = '\0';
break;
}
pos++;
}
return enc;
}
static void
derive_aes_key (struct GNUNET_CRYPTO_SymmetricSessionKey *key,
struct GNUNET_CRYPTO_SymmetricInitializationVector *iv,
struct GNUNET_HashCode *key_material)
{
static const char ctx_key[] = "reclaim-aes-ctx-key";
static const char ctx_iv[] = "reclaim-aes-ctx-iv";
GNUNET_CRYPTO_kdf (key,
sizeof(struct GNUNET_CRYPTO_SymmetricSessionKey),
ctx_key,
strlen (ctx_key),
key_material,
sizeof(struct GNUNET_HashCode),
NULL);
GNUNET_CRYPTO_kdf (iv,
sizeof(
struct GNUNET_CRYPTO_SymmetricInitializationVector),
ctx_iv,
strlen (ctx_iv),
key_material,
sizeof(struct GNUNET_HashCode),
NULL);
}
static void
calculate_key_priv (struct GNUNET_CRYPTO_SymmetricSessionKey *key,
struct GNUNET_CRYPTO_SymmetricInitializationVector *iv,
const struct GNUNET_CRYPTO_EcdsaPrivateKey *ecdsa_priv,
const struct GNUNET_CRYPTO_EcdhePublicKey *ecdh_pub)
{
struct GNUNET_HashCode key_material;
GNUNET_CRYPTO_ecdsa_ecdh (ecdsa_priv, ecdh_pub, &key_material);
derive_aes_key (key, iv, &key_material);
}
static void
calculate_key_pub (struct GNUNET_CRYPTO_SymmetricSessionKey *key,
struct GNUNET_CRYPTO_SymmetricInitializationVector *iv,
const struct GNUNET_CRYPTO_EcdsaPublicKey *ecdsa_pub,
const struct GNUNET_CRYPTO_EcdhePrivateKey *ecdh_priv)
{
struct GNUNET_HashCode key_material;
GNUNET_CRYPTO_ecdh_ecdsa (ecdh_priv, ecdsa_pub, &key_material);
derive_aes_key (key, iv, &key_material);
}
static void
decrypt_payload (const struct GNUNET_CRYPTO_EcdsaPrivateKey *ecdsa_priv,
const struct GNUNET_CRYPTO_EcdhePublicKey *ecdh_pub,
const char *ct,
size_t ct_len,
char *buf)
{
struct GNUNET_CRYPTO_SymmetricSessionKey key;
struct GNUNET_CRYPTO_SymmetricInitializationVector iv;
calculate_key_priv (&key, &iv, ecdsa_priv, ecdh_pub);
GNUNET_break (GNUNET_CRYPTO_symmetric_decrypt (ct, ct_len, &key, &iv, buf));
}
static void
encrypt_payload (const struct GNUNET_CRYPTO_EcdsaPublicKey *ecdsa_pub,
const struct GNUNET_CRYPTO_EcdhePrivateKey *ecdh_priv,
const char *payload,
size_t payload_len,
char *buf)
{
struct GNUNET_CRYPTO_SymmetricSessionKey key;
struct GNUNET_CRYPTO_SymmetricInitializationVector iv;
calculate_key_pub (&key, &iv, ecdsa_pub, ecdh_priv);
GNUNET_break (
GNUNET_CRYPTO_symmetric_encrypt (payload, payload_len, &key, &iv, buf));
}
/**
* Builds an OIDC authorization code including
* a reclaim ticket and nonce
*
* @param issuer the issuer of the ticket, used to sign the ticket and nonce
* @param ticket the ticket to include in the code
* @param attrs list of attributes which are shared
* @param nonce the nonce to include in the code
* @param code_challenge PKCE code challenge
* @return a new authorization code (caller must free)
*/
char *
OIDC_build_authz_code (const struct GNUNET_CRYPTO_EcdsaPrivateKey *issuer,
const struct GNUNET_RECLAIM_Ticket *ticket,
struct GNUNET_RECLAIM_ATTRIBUTE_ClaimList *attrs,
const char *nonce_str,
const char *code_challenge)
{
struct OIDC_Parameters params;
char *code_payload;
char *payload;
char *tmp;
char *code_str;
char *buf_ptr = NULL;
size_t payload_len;
size_t code_payload_len;
size_t attr_list_len = 0;
size_t code_challenge_len = 0;
uint32_t nonce;
uint32_t nonce_tmp;
struct GNUNET_CRYPTO_EccSignaturePurpose *purpose;
struct GNUNET_CRYPTO_EcdhePrivateKey *ecdh_priv;
struct GNUNET_CRYPTO_EcdhePublicKey ecdh_pub;
/** PLAINTEXT **/
// Assign ticket
memset (¶ms, 0, sizeof(params));
params.ticket = *ticket;
// Assign nonce
nonce = 0;
payload_len = sizeof(struct OIDC_Parameters);
if ((NULL != nonce_str) && (strcmp ("", nonce_str) != 0))
{
if ((1 != sscanf (nonce_str, "%u", &nonce)) || (nonce > UINT32_MAX))
{
GNUNET_break (0);
GNUNET_log (GNUNET_ERROR_TYPE_ERROR, "Invalid nonce %s\n", nonce_str);
return NULL;
}
GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
"Got nonce: %u from %s\n",
nonce,
nonce_str);
}
nonce_tmp = htonl (nonce);
params.nonce = nonce_tmp;
// Assign code challenge
if (NULL != code_challenge)
code_challenge_len = strlen (code_challenge);
payload_len += code_challenge_len;
params.code_challenge_len = htonl (code_challenge_len);
// Assign attributes
if (NULL != attrs)
{
// Get length
attr_list_len = GNUNET_RECLAIM_ATTRIBUTE_list_serialize_get_size (attrs);
params.attr_list_len = htonl (attr_list_len);
GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
"Length of serialized attributes: %lu\n",
attr_list_len);
// Get serialized attributes
payload_len += attr_list_len;
}
// Get plaintext length
payload = GNUNET_malloc (payload_len);
memcpy (payload, ¶ms, sizeof(params));
tmp = payload + sizeof(params);
if (0 < code_challenge_len)
{
memcpy (tmp, code_challenge, code_challenge_len);
tmp += code_challenge_len;
}
if (0 < attr_list_len)
GNUNET_RECLAIM_ATTRIBUTE_list_serialize (attrs, tmp);
/** END **/
/** ENCRYPT **/
// Get length
code_payload_len = sizeof(struct GNUNET_CRYPTO_EccSignaturePurpose)
+ sizeof(struct GNUNET_CRYPTO_EcdhePublicKey)
+ payload_len + sizeof(struct
GNUNET_CRYPTO_EcdsaSignature);
GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
"Length of data to encode: %lu\n",
code_payload_len);
// Generate ECDH key
ecdh_priv = GNUNET_CRYPTO_ecdhe_key_create ();
GNUNET_CRYPTO_ecdhe_key_get_public (ecdh_priv, &ecdh_pub);
// Initialize code payload
code_payload = GNUNET_malloc (code_payload_len);
GNUNET_assert (NULL != code_payload);
purpose = (struct GNUNET_CRYPTO_EccSignaturePurpose *) code_payload;
purpose->size = htonl (sizeof(struct GNUNET_CRYPTO_EccSignaturePurpose)
+ sizeof(ecdh_pub) + payload_len);
purpose->purpose = htonl (GNUNET_SIGNATURE_PURPOSE_RECLAIM_CODE_SIGN);
// Store pubkey
buf_ptr = (char *) &purpose[1];
memcpy (buf_ptr, &ecdh_pub, sizeof(ecdh_pub));
buf_ptr += sizeof(ecdh_pub);
// Encrypt plaintext and store
encrypt_payload (&ticket->audience, ecdh_priv, payload, payload_len, buf_ptr);
GNUNET_free (ecdh_priv);
GNUNET_free (payload);
buf_ptr += payload_len;
// Sign and store signature
if (GNUNET_SYSERR ==
GNUNET_CRYPTO_ecdsa_sign (issuer,
purpose,
(struct GNUNET_CRYPTO_EcdsaSignature *)
buf_ptr))
{
GNUNET_break (0);
GNUNET_log (GNUNET_ERROR_TYPE_ERROR, "Unable to sign code\n");
GNUNET_free (code_payload);
return NULL;
}
code_str = base64_and_urlencode (code_payload, code_payload_len);
GNUNET_free (code_payload);
return code_str;
}
/**
* Parse reclaim ticket and nonce from
* authorization code.
* This also verifies the signature in the code.
*
* @param audience the expected audience of the code
* @param code the string representation of the code
* @param code_verfier PKCE code verifier
* @param ticket where to store the ticket
* @param attrs the attributes in the code
* @param nonce where to store the nonce
* @return GNUNET_OK if successful, else GNUNET_SYSERR
*/
int
OIDC_parse_authz_code (const struct GNUNET_CRYPTO_EcdsaPrivateKey *ecdsa_priv,
const char *code,
const char *code_verifier,
struct GNUNET_RECLAIM_Ticket *ticket,
struct GNUNET_RECLAIM_ATTRIBUTE_ClaimList **attrs,
char **nonce_str)
{
char *code_payload;
char *ptr;
char *plaintext;
char *attrs_ser;
char *expected_code_challenge;
char *code_challenge;
char *code_verifier_hash;
struct GNUNET_CRYPTO_EccSignaturePurpose *purpose;
struct GNUNET_CRYPTO_EcdsaSignature *signature;
struct GNUNET_CRYPTO_EcdsaPublicKey ecdsa_pub;
struct GNUNET_CRYPTO_EcdhePublicKey *ecdh_pub;
uint32_t code_challenge_len;
uint32_t attrs_ser_len;
size_t plaintext_len;
size_t code_payload_len;
uint32_t nonce = 0;
struct OIDC_Parameters *params;
GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Trying to decode `%s'\n", code);
code_payload = NULL;
code_payload_len =
GNUNET_STRINGS_base64_decode (code, strlen (code), (void **) &code_payload);
if (code_payload_len < sizeof(struct GNUNET_CRYPTO_EccSignaturePurpose)
+ sizeof(struct GNUNET_CRYPTO_EcdhePublicKey)
+ sizeof(struct OIDC_Parameters)
+ sizeof(struct GNUNET_CRYPTO_EcdsaSignature))
{
GNUNET_log (GNUNET_ERROR_TYPE_ERROR, "Authorization code malformed\n");
GNUNET_free_non_null (code_payload);
return GNUNET_SYSERR;
}
purpose = (struct GNUNET_CRYPTO_EccSignaturePurpose *) code_payload;
plaintext_len = code_payload_len;
plaintext_len -= sizeof(struct GNUNET_CRYPTO_EccSignaturePurpose);
ptr = (char *) &purpose[1];
// Public ECDH key
ecdh_pub = (struct GNUNET_CRYPTO_EcdhePublicKey *) ptr;
ptr += sizeof(struct GNUNET_CRYPTO_EcdhePublicKey);
plaintext_len -= sizeof(struct GNUNET_CRYPTO_EcdhePublicKey);
// Decrypt ciphertext
plaintext_len -= sizeof(struct GNUNET_CRYPTO_EcdsaSignature);
plaintext = GNUNET_malloc (plaintext_len);
decrypt_payload (ecdsa_priv, ecdh_pub, ptr, plaintext_len, plaintext);
// ptr = plaintext;
ptr += plaintext_len;
signature = (struct GNUNET_CRYPTO_EcdsaSignature *) ptr;
params = (struct OIDC_Parameters *) plaintext;
// cmp code_challenge code_verifier
code_challenge_len = ntohl (params->code_challenge_len);
if (0 != code_challenge_len) /* Only check if this code requires a CV */
{
if (NULL == code_verifier)
{
GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
"Expected code verifier!\n");
GNUNET_free_non_null (code_payload);
return GNUNET_SYSERR;
}
code_verifier_hash = GNUNET_malloc (256 / 8);
// hash code verifier
gcry_md_hash_buffer (GCRY_MD_SHA256,
code_verifier_hash,
code_verifier,
strlen (code_verifier));
// encode code verifier
expected_code_challenge = base64url_encode (code_verifier_hash, 256 / 8);
code_challenge = (char *) ¶ms[1];
GNUNET_free (code_verifier_hash);
if ((strlen (expected_code_challenge) != code_challenge_len) ||
(0 !=
strncmp (expected_code_challenge, code_challenge, code_challenge_len)))
{
GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
"Invalid code verifier! Expected: %s, Got: %.*s\n",
expected_code_challenge,
code_challenge_len,
code_challenge);
GNUNET_free_non_null (code_payload);
GNUNET_free (expected_code_challenge);
return GNUNET_SYSERR;
}
GNUNET_free (expected_code_challenge);
}
// Ticket
memcpy (ticket, ¶ms->ticket, sizeof(params->ticket));
// Nonce
nonce = ntohl (params->nonce); // ntohl (*((uint32_t *) ptr));
GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Got nonce: %u\n", nonce);
// Signature
GNUNET_CRYPTO_ecdsa_key_get_public (ecdsa_priv, &ecdsa_pub);
if (0 != GNUNET_memcmp (&ecdsa_pub, &ticket->audience))
{
GNUNET_free (code_payload);
GNUNET_free (plaintext);
GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
"Audience in ticket does not match client!\n");
return GNUNET_SYSERR;
}
if (GNUNET_OK !=
GNUNET_CRYPTO_ecdsa_verify (GNUNET_SIGNATURE_PURPOSE_RECLAIM_CODE_SIGN,
purpose,
signature,
&ticket->identity))
{
GNUNET_free (code_payload);
GNUNET_free (plaintext);
GNUNET_log (GNUNET_ERROR_TYPE_ERROR, "Signature of AuthZ code invalid!\n");
return GNUNET_SYSERR;
}
// Attributes
attrs_ser = ((char *) ¶ms[1]) + code_challenge_len;
attrs_ser_len = ntohl (params->attr_list_len);
*attrs = GNUNET_RECLAIM_ATTRIBUTE_list_deserialize (attrs_ser, attrs_ser_len);
*nonce_str = NULL;
if (nonce != 0)
GNUNET_asprintf (nonce_str, "%u", nonce);
GNUNET_free (code_payload);
GNUNET_free (plaintext);
return GNUNET_OK;
}
/**
* Build a token response for a token request
* TODO: Maybe we should add the scope here?
*
* @param access_token the access token to include
* @param id_token the id_token to include
* @param expiration_time the expiration time of the token(s)
* @param token_response where to store the response
*/
void
OIDC_build_token_response (const char *access_token,
const char *id_token,
const struct GNUNET_TIME_Relative *expiration_time,
char **token_response)
{
json_t *root_json;
root_json = json_object ();
GNUNET_assert (NULL != access_token);
GNUNET_assert (NULL != id_token);
GNUNET_assert (NULL != expiration_time);
json_object_set_new (root_json, "access_token", json_string (access_token));
json_object_set_new (root_json, "token_type", json_string ("Bearer"));
json_object_set_new (root_json,
"expires_in",
json_integer (expiration_time->rel_value_us
/ (1000 * 1000)));
json_object_set_new (root_json, "id_token", json_string (id_token));
*token_response = json_dumps (root_json, JSON_INDENT (0) | JSON_COMPACT);
json_decref (root_json);
}
/**
* Generate a new access token
*/
char *
OIDC_access_token_new ()
{
char *access_token;
uint64_t random_number;
random_number =
GNUNET_CRYPTO_random_u64 (GNUNET_CRYPTO_QUALITY_NONCE, UINT64_MAX);
GNUNET_STRINGS_base64_encode (&random_number,
sizeof(uint64_t),
&access_token);
return access_token;
}