Hi @DeveshMishra,
If you're trying to call an external API from within Canvas LMS, the only way I know to do that would be through JavsScript uploaded to the Canvas account theme. I'd encourage you to try to develop a different approach though if this is an integration you're going to be trying to sell or offer to schools/institutions, because these types of integrations will face a lot of scrutiny, though this is required in some cases. You're going to need to be very careful with this, especially with a POST call, as you generally don't want to expose your auth token in plain text JavaScript.
Without knowing more details about your app, I'd still really encourage you to look at the LTI standard and try to make things work through that. The more normal situation would be to launch into an external app from Canvas using the API standard, then if the app itself needed more data than Canvas provided or needed to interact with the Canvas API, that would be done through an oAuth2 flow.
This is getting out of my area of expertise as an admin, but I'm sure some others can chime in here too and point you in a good direction.
-Chris