I have set up tomcat 8 according to this, and I have the following tomcat-users.xml file:
Correct answer can be found here
Looks like this issue can be reproduced while folowing mentioned tutorial on unix machines. Also noticed that author uses TC 8.0.33
Win (and OSX) do not have such issue, at least on my env:
Server version: Apache Tomcat/8.5.4
Server built: Jul 6 2016 08:43:30 UTC
Server number: 8.5.4.0
OS Name: Windows 8.1
OS Version: 6.3
Architecture: amd64
Java Home: C:\TOOLS\jdk1.8.0_101\jre
JVM Version: 1.8.0_101-b13
JVM Vendor: Oracle Corporation
CATALINA_BASE: C:\TOOLS\tomcat\apache-tomcat-8.5.4
CATALINA_HOME: C:\TOOLS\tomcat\apache-tomcat-8.5.4
After tomcat-users.xml is modified by adding role and user Tomcat Web Application Manager can be accessed on Tomcat/8.5.4.