apereo/cas · error · PreventedException

Unable to accept username

Error message

Unable to accept username 

What it means

BlockingPrincipalNameTransformer rejects the username because it matches the configured block/regex pattern; PreventedException is thrown so the username is never accepted downstream. This is a deliberate blocklist guard — the input at fault is the submitted username matching the forbidden pattern.

Solutions

1. Use a username that does not match the block pattern
2. Review the configured regex pattern; it may be overly broad and blocking legitimate users
3. If this is a policy check, handle PreventedException as an authentication rejection rather than a system error

When it happens

Trigger: Thrown at core/cas-server-core-util-api/src/main/java/org/apereo/cas/util/transforms/BlockingPrincipalNameTransformer.java:30 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of apereo/cas@e7288fc434 (2026-09-08). Data as JSON: /api/errors/fa64d18a3a04f7f3. Report an issue: GitHub.

Appendix: source

Thrown at core/cas-server-core-util-api/src/main/java/org/apereo/cas/util/transforms/BlockingPrincipalNameTransformer.java:30

 * and throws back an error if a match is found.
 *
 * @author Misagh Moayyed
 * @since 6.4.0
 */
@Setter
public class BlockingPrincipalNameTransformer implements PrincipalNameTransformer {

    private Pattern pattern;

    public BlockingPrincipalNameTransformer(final String pattern) {
        setPattern(RegexUtils.createPattern(pattern));
    }

    @Override
    public String transform(final String username) {
        val matcher = this.pattern.matcher(username);
        if (matcher.find()) {
            throw new PreventedException("Unable to accept username " + username);
        }
        return username.trim();
    }
}

View on GitHub (pinned to e7288fc434)