hadoop.security.key.provider.path is not documented.

The "Transparent Encryption in HDFS" page does not tell about this, but hdfs crypto operations failed with the below error.

There are no valid KeyProviders configured. No key
was created. You can use the -provider option to specify
a provider to use.

I have found hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/crypto/key/KeyProviderFactory.java uses this parameter.
By setting this parameter in core-site.xml, hdfs crypto commands runs successfully.