Add SHA256 support for digest auth

https://tools.ietf.org/html/rfc7616

src/mg_http_server.h

@@ -139,6 +139,14 @@ size_t mg_parse_multipart(const char *buf, size_t buf_len, char *var_name,
 int mg_get_http_var(const struct mg_str *buf, const char *name, char *dst,
                     size_t dst_len);
 
+/*
+ * Supported digest auth algorithms.
+ */
+enum mg_auth_algo {
+  MG_AUTH_ALGO_MD5 = 0,
+  MG_AUTH_ALGO_SHA256 = 1,
+};
+
 #if MG_ENABLE_FILESYSTEM
 /*
  * This structure defines how `mg_serve_http()` works.
@@ -175,6 +183,11 @@ struct mg_serve_http_opts {
    */
   const char *global_auth_file;
 
+  /*
+   * Password hashing algorithm used by the password files.
+   */
+  enum mg_auth_algo auth_algo;
+
   /* Set to "no" to disable directory listing. Enabled by default. */
   const char *enable_directory_listing;
 
@@ -426,6 +439,7 @@ struct mg_http_endpoint_opts {
   /* Authorization domain (realm) */
   const char *auth_domain;
   const char *auth_file;
+  enum mg_auth_algo auth_algo;
 };
 
 void mg_register_http_endpoint_opt(struct mg_connection *nc,
@@ -433,12 +447,23 @@ void mg_register_http_endpoint_opt(struct mg_connection *nc,
                                    mg_event_handler_t handler,
                                    struct mg_http_endpoint_opts opts);
 
+/*
+ * Sends 401 Unauthorized response.
+ */
+void mg_http_send_digest_auth_request(struct mg_connection *c,
+                                      const char *domain);
+void mg_http_send_digest_auth_request_algo(struct mg_connection *c,
+                                           const char *domain,
+                                           enum mg_auth_algo algo);
+
 /*
  * Authenticates a HTTP request against an opened password file.
  * Returns 1 if authenticated, 0 otherwise.
  */
 int mg_http_check_digest_auth(struct http_message *hm, const char *auth_domain,
                               FILE *fp);
+int mg_http_check_digest_auth_algo(struct http_message *hm, const char *auth_domain,
+                              enum mg_auth_algo fp_algo, FILE *fp);
 
 /*
  * Authenticates given response params against an opened password file.
@@ -451,6 +476,12 @@ int mg_check_digest_auth(struct mg_str method, struct mg_str uri,
                          struct mg_str response, struct mg_str qop,
                          struct mg_str nc, struct mg_str nonce,
                          struct mg_str auth_domain, FILE *fp);
+int mg_check_digest_auth_algo(struct mg_str method, struct mg_str uri,
+                              struct mg_str username, struct mg_str cnonce,
+                              struct mg_str response, struct mg_str qop,
+                              struct mg_str nc, struct mg_str nonce,
+                              struct mg_str auth_domain, enum mg_auth_algo algo,
+                              FILE *fp);
 
 /*
  * Sends buffer `buf` of size `len` to the client using chunked HTTP encoding.