question: return the secret key registered with the given application . this key is used to authenticate the executors before they can fetch shuffle files written by this application from the external shuffle service . if the specified application is not registered , return null . concode_field_sep ConcurrentHashMap<String,String> shuffleSecretMap concode_elem_sep Logger logger concode_elem_sep String SPARK_SASL_USER concode_field_sep void registerApp concode_elem_sep void registerApp concode_elem_sep void unregisterApp concode_elem_sep String getSaslUser
target: String function ( String arg0 ) { return shuffleSecretMap . get ( arg0 ) ; }