Endpoint creation

Created endpoint that receives user request and body. Creates a checkout 
session with Stripe and returns the clientSecret. 
Created Request and Response models.

server/src/service-layer/controllers/StripeCheckoutSession.ts

@@ -0,0 +1,34 @@
+import { StripeCheckoutRequestModel } from "service-layer/request-models/StripeCheckoutRequest"
+import { StripeCheckoutResponse } from "service-layer/response-models/StripeCheckoutResponse"
+import Stripe from "stripe"
+import { Controller, Post, Route, SuccessResponse, Request, Body } from "tsoa"
+
+@Route("create-checkout-session")
+export class CreateCheckoutSession extends Controller {
+  @Post()
+  @SuccessResponse(200, "Successful checkout session creation")
+  public async createCheckoutSession(
+    @Request() request: any,
+    @Body() requestBody: StripeCheckoutRequestModel
+  ): Promise<StripeCheckoutResponse> {
+    const stripe = new Stripe(process.env.STRIPE_API_KEY)
+    try {
+      const session = await stripe.checkout.sessions.create({
+        // consumer changeable
+        client_reference_id: requestBody.client_reference_id,
+        return_url: requestBody.return_url,
+        line_items: [requestBody.line_item],
+        metadata: requestBody.metadata,
+        // configured internally and should not change
+        ui_mode: "embedded",
+        mode: "payment",
+        currency: "NZD"
+      })
+      this.setStatus(200)
+      return { clientSecret: session.client_secret }
+    } catch (e) {
+      this.setStatus(400)
+      return { clientSecret: null }
+    }
+  }
+}

server/src/service-layer/request-models/StripeCheckoutRequest.ts

@@ -0,0 +1,9 @@
+export interface StripeCheckoutRequestModel {
+  client_reference_id: string
+  return_url: string
+  line_item: {
+    price: string
+    quanitity: number
+  }
+  metadata: any
+}

server/src/service-layer/response-models/StripeCheckoutResponse.ts

@@ -0,0 +1,3 @@
+export interface StripeCheckoutResponse {
+  clientSecret: string
+}