OAuth part

The minimum to pass all authentications and arrive at the embedded app
index. This library is to be used with shopify-app-template-c for now,
as it assumes the existence of shopify.app.toml in the parent directory,
and index.html in the frontend directory.

1 files changed, 34 insertions, 0 deletions

diff --git a/crypt.h b/crypt.h
new file mode 100644
index 0000000..f836bcc
--- /dev/null
+++ b/crypt.h
@@ -0,0 +1,34 @@
+#include <gcrypt.h>
+
+static inline void crypt_init()
+{
+	gcry_check_version("1.9.4");
+}
+
+static inline bool crypt_maccmp(const char *key, const char *query,
+		const char *hmac)
+{
+	gcry_mac_hd_t hd;
+	gcry_mac_open(&hd, GCRY_MAC_HMAC_SHA256, GCRY_MAC_FLAG_SECURE, NULL);
+	gcry_mac_setkey(hd, key, strlen(key));
+	gcry_mac_write(hd, query, strlen(query));
+	size_t hmac_sha256_len = 32;
+	unsigned char hmac_sha256[hmac_sha256_len + 1];
+	gcry_mac_read(hd, hmac_sha256, &hmac_sha256_len);
+	gcry_mac_close(hd);
+	char hmac_sha256_str[65] = { [0] = '\0' };
+	for (int i = 0; i < hmac_sha256_len; i++)
+		sprintf(hmac_sha256_str, "%s%02x", hmac_sha256_str,
+				hmac_sha256[i]);
+	return !strcmp(hmac, hmac_sha256_str);
+}
+
+static inline void crypt_getnonce(char *string, const size_t string_len)
+{
+	string[0] = '\0';
+	const size_t nonce_len = string_len / 2;
+	unsigned char nonce[nonce_len + 1];
+	gcry_create_nonce(nonce, nonce_len);
+	for (int i = 0; i < nonce_len; i++)
+		sprintf(string, "%s%02x", string, nonce[i]);
+}