Error "Unable to Sign In" With SAML SSO When IDP-Side Username Contains Non-English Characters

Issue

When Tableau Server has been configured for SAML authentication and the username in SAML response contains non-English characters, users cannot sign in to Tableau Server.

The following SAML errors are logged in \vizportal\vizportal-<n>.log

ERROR com.tableausoftware.samlauthentication.model.XPathUtils - Failed to evaluate XPATH in the provided input

org.xml.sax.SAXParseException: Invalid byte 1 of 1-byte UTF-8 sequence.

or
org.xml.sax.SAXParseException: Invalid byte 2 of 3-byte UTF-8 sequence.

Environment

Tableau Server 2020.4.0, 2020.4.1

Resolution

Workaround1:
Change the user name to English when adding a user on the IDP-side,

Workaround2:
Use Tableau Server 2020.3.x or an earlier version.