Clients getting Error 400 bad request

Document ID : KB000101845
Last Modified Date : 15/06/2018
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Client -> CA Access gateway (SPS) R12.7 -> APIM Gateway (OAuth) 9.2
Error 400 reported in logs of CA Access gateway no entries in APIM Gateway

Trouble shooting the client error from APIM gateway side is not possible because of the lack of any logging 
HTTP logs from the tomcat (and coyote) libraries are disabled in the Gateway.
Adding logging to SSG log for Error 400

1. Go to Tasks > Logging and Auditing > Manage Log/Audit Sinks > ssg > Properties. Set the Severity Threshhold to FINE.

2. Go to Tasks > Global Settings > Manage Cluster Wide Properties > Add a new CWP log.levels. Modify the value of "com.l7tech.level = FINE" and add new value "org.apache.coyote.http11.Http11Processor.level = FINE".

Now this error can be observed in the Gateway logs: org.apache.coyote.http11.Http11Processor: Error parsing HTTP request header java.lang.IllegalArgumentException: Request header is too large ...