Lumen JWT auth returns false

I am trying to build an api with an existing database which has email and password column as laravel's auth driver requires as according to my understanding. The password saved in the users table is saved in an encrypted form using php's inbuilt sha1() tecnique. But when i try to login using the auth->attempt() method, instead of getting a token i see is false returned. I followed from the http://laravelista.com/json-web-token-authentication-for-lumen source any help would be time saving.