DRAFT KB-XXXX Users are unable to login to Appian with exception, "java.lang.IllegalArgumentException: Invalid character found in method name. HTTP method names must be tokens"

Symptoms

All users are unable to login to Appian with the message:

'Error401 - Unauthorized: Sorry, your request could not be processed'

Tomcat logs the following in <APPIAN_HOME>/logs/tomcat-stdOut.log: 

Error parsing HTTP request header
java.lang.IllegalArgumentException: Invalid character found in method name. HTTP method names must be tokens

Cause

The conf.suite.SCHEME property is incorrectly configured in <APPIAN_HOME>/conf/custom.properties.

Action

1. Ensure custom.properties is configured according to installation documentation so that the line conf.suite.SCHEME is uncommented and set to the correct value.

2. Restart Tomcat.

Affected Versions

This article applies to Appian 18.3 and later.