How to use Pluggable RPC authentication

[陈叶超]

Hi all:

in https://issues.apache.org/jira/browse/HBASE-23347 introduce a puuggable
rpc authentication

https://github.com/apache/hbase/pull/884

I want to use this pr to create a custom auth

how to use or config the custom authentication ?

I check the test code ,why we need setUp kerberos first?

and seems server offer three simple/gss/ Digest and  extras auth*

if i add a extras but the client use simple

the auth can be by pass

now i just set three properties :

hbase.client.sasl.provider.class

hbase.client.sasl.provider.extras

hbase.server.sasl.provider.extras

what i missed?

I check the code

in ServerRpcConnection.java


```java
//from me: if client pass the simple authbyte? we just use simple???
 this.provider = this.saslProviders.selectProvider(authbyte);
    if (this.provider == null) {
      String msg = getFatalConnectionString(version, authbyte);
      doBadPreambleHandling(msg, new BadAuthException(msg));
      return false;
    }
    //from me : don't understand here
    // TODO this is a wart while simple auth'n doesn't go through sasl.
   if (this.rpcServer.isSecurityEnabled && isSimpleAuthentication()) {
      if (this.rpcServer.allowFallbackToSimpleAuth) {
        this.rpcServer.metrics.authenticationFallback();
        authenticatedWithFallback = true;
      } else {
        AccessDeniedException ae = new
AccessDeniedException("Authentication is required");
        doRespond(getErrorResponse(ae.getMessage(), ae));
        return false;
      }
    }
      //from me : don't understand here ?
     if (!this.rpcServer.isSecurityEnabled && !isSimpleAuthentication()) {
      doRawSaslReply(SaslStatus.SUCCESS, new
IntWritable(SaslUtil.SWITCH_TO_SIMPLE_AUTH), null,
        null);
      provider = saslProviders.getSimpleProvider();
      // client has already sent the initial Sasl message and we
      // should ignore it. Both client and server should fall back
      // to simple auth from now on.
      skipInitialSaslHandshake = true;
    }
    useSasl = true;

```