Most likely the issue is not related to Tosca REST API, rather is a CORS problem. So, I am assuming your web server and the Tosca REST API server are on different domain. You can basically bypass this problem by allowing cross-origin requests from the web application, by adding the following configuration to the web.config
<system.webServer>
<httpProtocol>
<customHeaders>
<add name="Access-Control-Allow-Headers" value="Content-Type" />
<add name="Access-Control-Allow-Methods" value="GET, POST" />
<add name="Access-Control-Allow-Origin" value="*" />
</customHeaders>
</httpProtocol>
</system.webServer>
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