auth.c

#include "internal.h"

// Stringify binary data. Output buffer must be twice as big as input,
// because each byte takes 2 bytes in string representation
static void bin2str(char *to, const unsigned char *p, size_t len) {
  static const char *hex = "0123456789abcdef";

  for (; len--; p++) {
    *to++ = hex[p[0] >> 4];
    *to++ = hex[p[0] & 0x0f];
  }
  *to = '\0';
}

// Return stringified MD5 hash for list of strings. Buffer must be 33 bytes.
char *mg_md5(char buf[33], ...) {
  unsigned char hash[16];
  const char *p;
  va_list ap;
  MD5_CTX ctx;

  MD5Init(&ctx);

  va_start(ap, buf);
  while ((p = va_arg(ap, const char *)) != NULL) {
    MD5Update(&ctx, (const unsigned char *) p, (unsigned) strlen(p));
  }
  va_end(ap);

  MD5Final(hash, &ctx);
  bin2str(buf, hash, sizeof(hash));
  return buf;
}

// Check the user's password, return 1 if OK
static int check_password(const char *method, const char *ha1, const char *uri,
                          const char *nonce, const char *nc, const char *cnonce,
                          const char *qop, const char *response) {
  char ha2[32 + 1], expected_response[32 + 1];

  // Some of the parameters may be NULL
  if (method == NULL || nonce == NULL || nc == NULL || cnonce == NULL ||
      qop == NULL || response == NULL) {
    return 0;
  }

  // NOTE(lsm): due to a bug in MSIE, we do not compare the URI
  // TODO(lsm): check for authentication timeout
  if (// strcmp(dig->uri, c->ouri) != 0 ||
      strlen(response) != 32
      // || now - strtoul(dig->nonce, NULL, 10) > 3600
      ) {
    return 0;
  }

  mg_md5(ha2, method, ":", uri, NULL);
  mg_md5(expected_response, ha1, ":", nonce, ":", nc,
      ":", cnonce, ":", qop, ":", ha2, NULL);

  return mg_strcasecmp(response, expected_response) == 0;
}

// Use the global passwords file, if specified by auth_gpass option,
// or search for .htpasswd in the requested directory.
static FILE *open_auth_file(struct mg_connection *conn, const char *path) {
  char name[PATH_MAX];
  const char *p, *e, *gpass = conn->ctx->config[GLOBAL_PASSWORDS_FILE];
  struct file file = STRUCT_FILE_INITIALIZER;
  FILE *fp = NULL;

  if (gpass != NULL) {
    // Use global passwords file
    fp = mg_fopen(gpass, "r");
    // Important: using local struct file to test path for is_directory flag.
    // If filep is used, mg_stat() makes it appear as if auth file was opened.
  } else if (mg_stat(path, &file) && file.is_directory) {
    mg_snprintf(name, sizeof(name), "%s%c%s",
                path, '/', PASSWORDS_FILE_NAME);
    fp = mg_fopen(name, "r");
  } else {
     // Try to find .htpasswd in requested directory.
    for (p = path, e = p + strlen(p) - 1; e > p; e--)
      if (e[0] == '/')
        break;
    mg_snprintf(name, sizeof(name), "%.*s%c%s",
                (int) (e - p), p, '/', PASSWORDS_FILE_NAME);
    fp = mg_fopen(name, "r");
  }

  return fp;
}

// Parsed Authorization header
struct ah {
  char *user, *uri, *cnonce, *response, *qop, *nc, *nonce;
};

// Return 1 on success. Always initializes the ah structure.
static int parse_auth_header(struct mg_connection *conn, char *buf,
                             size_t buf_size, struct ah *ah) {
  char *name, *value, *s;
  const char *auth_header;

  (void) memset(ah, 0, sizeof(*ah));
  if ((auth_header = mg_get_header(conn, "Authorization")) == NULL ||
      mg_strncasecmp(auth_header, "Digest ", 7) != 0) {
    return 0;
  }

  // Make modifiable copy of the auth header
  (void) mg_strlcpy(buf, auth_header + 7, buf_size);
  s = buf;

  // Parse authorization header
  for (;;) {
    // Gobble initial spaces
    while (isspace(* (unsigned char *) s)) {
      s++;
    }
    name = skip_quoted(&s, "=", " ", 0);
    // Value is either quote-delimited, or ends at first comma or space.
    if (s[0] == '\"') {
      s++;
      value = skip_quoted(&s, "\"", " ", '\\');
      if (s[0] == ',') {
        s++;
      }
    } else {
      value = skip_quoted(&s, ", ", " ", 0);  // IE uses commas, FF uses spaces
    }
    if (*name == '\0') {
      break;
    }

    if (!strcmp(name, "username")) {
      ah->user = value;
    } else if (!strcmp(name, "cnonce")) {
      ah->cnonce = value;
    } else if (!strcmp(name, "response")) {
      ah->response = value;
    } else if (!strcmp(name, "uri")) {
      ah->uri = value;
    } else if (!strcmp(name, "qop")) {
      ah->qop = value;
    } else if (!strcmp(name, "nc")) {
      ah->nc = value;
    } else if (!strcmp(name, "nonce")) {
      ah->nonce = value;
    }
  }

  // CGI needs it as REMOTE_USER
  if (ah->user != NULL) {
    conn->request_info.remote_user = mg_strdup(ah->user);
  } else {
    return 0;
  }

  return 1;
}

// Authorize against the opened passwords file. Return 1 if authorized.
static int authorize(struct mg_connection *conn, FILE *fp) {
  struct ah ah;
  char line[256], f_user[256], ha1[256], f_domain[256], buf[MG_BUF_LEN];

  if (!parse_auth_header(conn, buf, sizeof(buf), &ah)) {
    return 0;
  }

  // Loop over passwords file
  while (fgets(line, sizeof(line), fp) != NULL) {
    if (sscanf(line, "%[^:]:%[^:]:%s", f_user, f_domain, ha1) != 3) {
      continue;
    }

    if (!strcmp(ah.user, f_user) &&
        !strcmp(conn->ctx->config[AUTHENTICATION_DOMAIN], f_domain))
      return check_password(conn->request_info.request_method, ha1, ah.uri,
                            ah.nonce, ah.nc, ah.cnonce, ah.qop, ah.response);
  }

  return 0;
}

// Return 1 if request is authorised, 0 otherwise.
static int check_authorization(struct mg_connection *conn, const char *path) {
  char fname[PATH_MAX];
  struct vec uri_vec, filename_vec;
  const char *list;
  FILE *fp = NULL;
  int authorized = 1;

  list = conn->ctx->config[PROTECT_URI];
  while ((list = next_option(list, &uri_vec, &filename_vec)) != NULL) {
    if (!memcmp(conn->request_info.uri, uri_vec.ptr, uri_vec.len)) {
      mg_snprintf(fname, sizeof(fname), "%.*s",
                  (int) filename_vec.len, filename_vec.ptr);
      fp = mg_fopen(fname, "r");
      break;
    }
  }

  if (fp == NULL) {
    fp = open_auth_file(conn, path);
  }

  if (fp != NULL) {
    authorized = authorize(conn, fp);
    fclose(fp);
  }

  return authorized;
}

static void send_authorization_request(struct mg_connection *conn) {
  conn->status_code = 401;
  mg_printf(conn,
            "HTTP/1.1 401 Unauthorized\r\n"
            "Content-Length: 0\r\n"
            "WWW-Authenticate: Digest qop=\"auth\", "
            "realm=\"%s\", nonce=\"%lu\"\r\n\r\n",
            conn->ctx->config[AUTHENTICATION_DOMAIN],
            (unsigned long) time(NULL));
}

static int is_authorized_for_put(struct mg_connection *conn) {
  const char *passfile = conn->ctx->config[PUT_DELETE_PASSWORDS_FILE];
  FILE *fp;
  int ret = 0;

  if (passfile != NULL && (fp = mg_fopen(passfile, "r")) != NULL) {
    ret = authorize(conn, fp);
    fclose(fp);
  }

  return ret;
}

int mg_modify_passwords_file(const char *fname, const char *domain,
                             const char *user, const char *pass) {
  int found;
  char line[512], u[512], d[512], ha1[33], tmp[PATH_MAX];
  FILE *fp, *fp2;

  found = 0;
  fp = fp2 = NULL;

  // Regard empty password as no password - remove user record.
  if (pass != NULL && pass[0] == '\0') {
    pass = NULL;
  }

  (void) snprintf(tmp, sizeof(tmp), "%s.tmp", fname);

  // Create the file if does not exist
  if ((fp = fopen(fname, "a+")) != NULL) {
    fclose(fp);
  }

  // Open the given file and temporary file
  if ((fp = fopen(fname, "r")) == NULL) {
    return 0;
  } else if ((fp2 = fopen(tmp, "w+")) == NULL) {
    fclose(fp);
    return 0;
  }

  // Copy the stuff to temporary file
  while (fgets(line, sizeof(line), fp) != NULL) {
    if (sscanf(line, "%[^:]:%[^:]:%*s", u, d) != 2) {
      continue;
    }

    if (!strcmp(u, user) && !strcmp(d, domain)) {
      found++;
      if (pass != NULL) {
        mg_md5(ha1, user, ":", domain, ":", pass, NULL);
        fprintf(fp2, "%s:%s:%s\n", user, domain, ha1);
      }
    } else {
      fprintf(fp2, "%s", line);
    }
  }

  // If new user, just add it
  if (!found && pass != NULL) {
    mg_md5(ha1, user, ":", domain, ":", pass, NULL);
    fprintf(fp2, "%s:%s:%s\n", user, domain, ha1);
  }

  // Close files
  fclose(fp);
  fclose(fp2);

  // Put the temp file in place of real file
  remove(fname);
  rename(tmp, fname);

  return 1;
}