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# Large Fiat headers can cause permission errors due to timeouts and 400 errors.

### Issue <a href="#issue" id="issue"></a>

If a header is passed to Fiat that is too big in size, it can cause errors in the logs such as below `java.lang.IllegalArgumentException: Request header is too large`

### Cause <a href="#cause" id="cause"></a>

The default header size for Tomcat is only 8KB. If this limit is exceeded, Fiat will timeout and throw `400 errors` as it is unable to parse the entire header.