In case you use a proxy with authentication, go to
<tomcat_path>/WEB-INF/classes/configuration.properties file
and uncomment the following lines:
- proxy with the HTTP protocol:
#http.proxyUser=someuser
#http.proxyPassword=somepassword
- proxy with the HTTPS protocol:
#https.proxyUser=someuser
#https.proxyPassword=somepassword
For more information about proxy configuration, see
https://docs.oracle.com/javase/8/docs/technotes/guides/net/proxies.html.