Configuring Keycloak provider with SPI

I am trying to configure one of my providers factory (its ID is "phone-verification") with the following code :

@Overridepublic void init(Config.Scope config) {    String lifespan = config.get("lifespan");    logger.warn("Lifespan : " + lifespan);}

And I have my configuration done in standalone.xml with the following property :

<spi name="phoneVerification"><default-provider>phone-verification</default-provider><provider name="phone-verification" enabled="true"><properties><property name="lifespan" value="2592000"/></properties></provider></spi

However config.get("lifespan") always returns null. Is there any extra step or am I doing anything wrong ?

NOTE : I specified the config file with the /keycloak/bin/standalone.sh --server-config=standalone.xml.