RANGER-5499: Set ranger-admin header authn cfg values to null

[kumaab]

What changes were proposed in this pull request?

The header based authentication configs must be set explicitly when Ranger is deployed in an environment with trusted proxy.

How was this patch tested?

CI

[mneethiraj]

@kumaab - in addition to these updates, consider updating RangerHeaderPreAuthFilter.initialize() as shown below:

protected void initialize() {
    headerAuthEnabled = PropertiesUtil.getBooleanProperty(PROP_HEADER_AUTH_ENABLED, false);

    if (headerAuthEnabled) {
        userNameHeaderName = PropertiesUtil.getProperty(PROP_USERNAME_HEADER_NAME);

        if (StringUtils.isBlank(userNameHeaderName)) {
            LOG.warn("Disabling header-based authentication, as configuration {} is not set", PROP_USERNAME_HEADER_NAME);

            headerAuthEnabled = false;
        }
    }
}

[kumaab]

@kumaab - in addition to these updates, consider updating RangerHeaderPreAuthFilter.initialize() as shown below:

protected void initialize() {
    headerAuthEnabled = PropertiesUtil.getBooleanProperty(PROP_HEADER_AUTH_ENABLED, false);

    if (headerAuthEnabled) {
        userNameHeaderName = PropertiesUtil.getProperty(PROP_USERNAME_HEADER_NAME);

        if (StringUtils.isBlank(userNameHeaderName)) {
            LOG.warn("Disabling header-based authentication, as configuration {} is not set", PROP_USERNAME_HEADER_NAME);

            headerAuthEnabled = false;
        }
    }
}

Sure, makes sense, updated!