Installation/SetUp

Install the package: go get -u github.com/gorilla/mux
This helps in creating go routers

Installing go-jwt package:
go get github.com/dgrijalva/jwt-go

PQ package: which helps us connect to PostGre DB
go get github.com/lib/pq

BCRYPT package: This is part of the go installation
or else : go get golang.org/x/crypto/bcrypt

Go Spew: Could be used for printing detailed struct formats
go get -u github.com/davecgh/go-spew/spew

gotenv: To use the environment variables
go get github.com/subosito/gotenv

JWT

JSON  Web Token
Means of exchanging information between 2 parties
Digitally Signed

Structure: {Base64 encoder Header}.{Base64 encoder Payload}.{Signature}
Header: Consists of Alg &, Token Type --> {"alg": "HS256", "type":"JWT"}
Payload: Payload carry the claims
    - User &, additional data such as expiry
    - Types of claims: Registered, Public &, Private
    - eg: {"email":"abc@abc.com", "Issuer": "course"}
Signature: Computed from Header, Payload &, a secret 
    - Generated by the algo mentioned in the header
    - Digitally signed using a secret only known to the developer
    - Cannot be decrypted unless you have the access to secret

PostGres SQL

For the tutorial we will PostGresSQL as a service.
URL: https://www.elephantsql.com
Create an instance [Free one] ->
To create a user table:
    create table users (
    id serial primary key,
    email text not null unique,
    password text not null
    );
To insert records:
    insert into users (email, password) values ('abc@gmail.com', '123456');
    insert into users (email, password) values ('xyz@gmail.com', '123456');
To select records:
    SELECT * FROM "public"."users"

Running the application

go build
./go-jwt

The services would available at port 8000
For example: 
POST: http://localhost:8000/singup
Sample Request Json: {
"email": "user6@abc.com",
"password": "1234"
}