@nitishdola .env isn't (or shouldn't!!!!) be accessible from your website as a direct path (it isn't by default).
The only files you can directly access as part of your URI are whatever's within the 'public' directory, everything else is safe.
If you really want to do this, the following should work (untested):
'mysql' => [
'driver' => 'mysql',
'host' => 'localhost',
'database' => 'database_name',
'username' => 'db_username',
'password' => 'my_secret_passwd',
'charset' => 'utf8',
'collation' => 'utf8_unicode_ci',
'prefix' => '',
'strict' => false,
],
Notice that the 'env()' call has completely been replaced by a simple string. This should prevent anything from being read from the .env file.
Cheers..
Ian
EDIT: Alternatively, removing the DB_* lines completely from your .env file should then use the defaults (second param in the env() calls).