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/*
* nanobbs, a tiny forums software.
* Copyright (C) 2025-2026 Xavier Del Campo Romero
*
* This program 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.
*
* This program 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 <https://www.gnu.org/licenses/>.
*/
#include "jwt.h"
#include <dynstr.h>
#include <sodium.h>
#include <errno.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#define VARIANT sodium_base64_VARIANT_URLSAFE
static char *b64(const void *const p, const size_t len)
{
char *ret = NULL;
const size_t n = sodium_base64_encoded_len(len, VARIANT);
if (!(ret = malloc(n)))
{
fprintf(stderr, "%s: malloc(3): %s\n", __func__, strerror(errno));
return NULL;
}
else if (!sodium_bin2base64(ret, n, p, len, VARIANT))
{
fprintf(stderr, "%s: sodium_bin2base64 failed\n", __func__);
free(ret);
return NULL;
}
return ret;
}
static int b64d(const char *const b64, const size_t len, void **const outbuf,
size_t *const outsz)
{
int ret = 1;
size_t sz = 0, binlen;
const char *end;
void *buf = NULL, *p;
again:
if (!(p = realloc(buf, ++sz)))
{
fprintf(stderr, "%s: realloc(3): %s\n", __func__, strerror(errno));
goto failure;
}
else if (sodium_base642bin(buf = p, sz, b64, len, NULL, &binlen, &end,
VARIANT))
{
if (errno == ERANGE)
goto again;
fprintf(stderr, "%s: sodium_base642bin failed\n", __func__);
goto failure;
}
*outbuf = buf;
*outsz = sz;
return 0;
failure:
free(buf);
return ret;
}
static char *get_hmac(const void *const buf, const size_t n,
const void *const key, const size_t keyn)
{
unsigned char hmac[crypto_auth_hmacsha256_KEYBYTES];
char *ret;
if (keyn != crypto_auth_hmacsha256_KEYBYTES)
{
fprintf(stderr, "%s: invalid key size (%zu), expected %u\n", __func__,
n, crypto_auth_hmacsha256_KEYBYTES);
return NULL;
}
else if (crypto_auth_hmacsha256(hmac, buf, n, key))
{
fprintf(stderr, "%s: HMAC failed\n", __func__);
return NULL;
}
else if (!(ret = b64(hmac, sizeof hmac)))
fprintf(stderr, "%s: b64 failed\n", __func__);
return ret;
}
char *jwt_encode(const cJSON *const j, const void *const key, const size_t n)
{
static const char jwt_header[] = "{\"alg\": \"HS256\", \"typ\": \"JWT\"}";
struct dynstr d;
char *ret = NULL, *p = NULL, *header = NULL, *hmac = NULL, *encp = NULL;
dynstr_init(&d);
if (!(p = cJSON_PrintUnformatted(j)))
{
fprintf(stderr, "%s: cJSON_PrintUnformatted failed\n", __func__);
goto end;
}
else if (!(encp = b64(p, strlen(p))))
{
fprintf(stderr, "%s: b64 %s failed\n", __func__, p);
goto end;
}
else if (!(header = b64(jwt_header, strlen(jwt_header))))
{
fprintf(stderr, "%s: b64 %s failed\n", __func__, jwt_header);
}
else if (dynstr_append(&d, "%s.%s", header, encp))
{
fprintf(stderr, "%s: dynstr_append header+payload failed", __func__);
goto end;
}
else if (!(hmac = get_hmac(d.str, d.len, key, n)))
{
fprintf(stderr, "%s: get_hmac failed\n", __func__);
goto end;
}
else if (dynstr_append(&d, ".%s", hmac))
{
fprintf(stderr, "%s: dynstr_append hmac failed\n", __func__);
goto end;
}
ret = d.str;
end:
free(header);
free(hmac);
free(encp);
cJSON_free(p);
if (!ret)
dynstr_free(&d);
return ret;
}
static size_t cnt(const char *s, const char c)
{
size_t ret = 0;
while (*s)
if (*s++ == c)
ret++;
return ret;
}
int jwt_decode(const char *const jwt, const void *const key, const size_t n,
cJSON **const payload)
{
int ret = 1;
cJSON *j = NULL;
void *p = NULL;
const char *first = strchr(jwt, '.'), *const last = strrchr(jwt, '.');
const unsigned char *const in = (const unsigned char *)jwt;
unsigned char hmac[crypto_auth_hmacsha256_KEYBYTES];
size_t sz;
if (n != crypto_auth_hmacsha256_KEYBYTES)
{
fprintf(stderr, "%s: invalid key size (%zu), expected %u\n", __func__,
n, crypto_auth_hmacsha256_KEYBYTES);
ret = -1;
goto end;
}
else if (cnt(jwt, '.') != 2 || ++first == last)
goto end;
else if (sodium_base642bin(hmac, sizeof hmac, last + 1, strlen(last + 1),
NULL, NULL, NULL, VARIANT))
{
fprintf(stderr, "%s: sodium_base642bin failed\n", __func__);
goto end;
}
else if (crypto_auth_hmacsha256_verify(hmac, in, last - jwt, key))
{
fprintf(stderr, "%s: crypto_auth_hmacsha256_verify failed\n", __func__);
goto end;
}
else if ((ret = b64d(first, last - first, &p, &sz)))
{
if (ret < 0)
fprintf(stderr, "%s: b64d failed\n", __func__);
goto end;
}
else if (!(j = cJSON_ParseWithLength(p, sz)))
{
fprintf(stderr, "%s: cJSON_ParseWithLength failed\n", __func__);
goto end;
}
else if (!cJSON_IsObject(j))
{
fprintf(stderr, "%s: cJSON_IsObject failed\n", __func__);
goto end;
}
*payload = j;
ret = 0;
end:
if (ret)
cJSON_Delete(j);
free(p);
return ret;
}
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