Hi Anupam1989,
I am only starting to use the REST API two weeks ago.
You have GET and POST requests. In case you are logged in. You just can open a new browser tab and copy the URL of the GET request you want to issue.
Since you are authenticated/login within the browser the request will be processed without asking for credentials.
You can do the same via windows comandline using curl.exe (built in in win10). E.g.
curl -D- -u XXXXX:YYYYY -X GET -H "X-Atlassian-Token: no-check" https://jira-test.xxxx.de/rest/zapi/latest/cycle?projectId=14145
You have to replace XXXX and YYYYY with your Jira Username and Password.
Of course it is no valid approach to hardcode your user credentials within a script. In case you omit ":YYYY" you will be prompted for the password.
I am currently looking for a way to use another more secure authentification mechanism (tokens?), which can be used for an impersonate access within scripts.
Can you give some more details: OS Windows or Linux, Script/Programming Language to be used for REST communication: Python, Perl, Java, ...
Best regards, Raphael