chore(refactor): split up and add tests for core functionality

src/auth/refreshTokens.ts

@@ -0,0 +1,49 @@
+import { SasAuthResponse } from '@sasjs/utils/types'
+import { prefixMessage } from '@sasjs/utils/error'
+import * as NodeFormData from 'form-data'
+import { RequestClient } from '../request/RequestClient'
+
+/**
+ * Exchanges the refresh token for an access token for the given client.
+ * @param requestClient - the pre-configured HTTP request client
+ * @param clientId - the client ID to authenticate with.
+ * @param clientSecret - the client secret to authenticate with.
+ * @param authCode - the refresh token received from the server.
+ */
+export async function refreshTokens(
+  requestClient: RequestClient,
+  clientId: string,
+  clientSecret: string,
+  refreshToken: string
+) {
+  const url = '/SASLogon/oauth/token'
+  let token
+  token =
+    typeof Buffer === 'undefined'
+      ? btoa(clientId + ':' + clientSecret)
+      : Buffer.from(clientId + ':' + clientSecret).toString('base64')
+
+  const headers = {
+    Authorization: 'Basic ' + token
+  }
+
+  const formData =
+    typeof FormData === 'undefined' ? new NodeFormData() : new FormData()
+  formData.append('grant_type', 'refresh_token')
+  formData.append('refresh_token', refreshToken)
+
+  const authResponse = await requestClient
+    .post<SasAuthResponse>(
+      url,
+      formData,
+      undefined,
+      'multipart/form-data; boundary=' + (formData as any)._boundary,
+      headers
+    )
+    .then((res) => res.result)
+    .catch((err) => {
+      throw prefixMessage(err, 'Error while refreshing tokens')
+    })
+
+  return authResponse
+}