What does a variable declaration like this mean - uint32_t (* name)(something, something, something) in C

Question

struct AzureIoTHubClient{
struct{
    AzureIoTMQTT_t xMQTTContext;

    uint8_t * pucWorkingBuffer;
    uint32_t ulWorkingBufferLength;
    az_iot_hub_client xAzureIoTHubClientCore;

    const uint8_t * pucHostname;
    uint16_t ulHostnameLength;
    const uint8_t * pucDeviceID;
    uint16_t ulDeviceIDLength;
    const uint8_t * pucSymmetricKey;
    uint32_t ulSymmetricKeyLength;

    uint32_t ( * pxTokenRefresh )( AzureIoTHubClient_t * pxAzureIoTHubClient,
                                   uint64_t ullExpiryTimeSecs,
                                   const uint8_t * ucKey,
                                   uint32_t ulKeyLen,
                                   uint8_t * pucSASBuffer,
                                   uint32_t ulSasBufferLen,
                                   uint32_t * pulSaSLength );
    AzureIoTGetHMACFunc_t xHMACFunction;
    AzureIoTGetCurrentTimeFunc_t xTimeFunction;
    AzureIoTTelemetryAckCallback_t xTelemetryCallback;

    uint32_t ulCurrentPropertyRequestID;

    AzureIoTHubClientReceiveContext_t xReceiveContext[ azureiothubSUBSCRIBE_FEATURE_COUNT ];
}
_internal; /**< @brief Internal to the SDK */};

This is the structure defined in Azure's Middleware for FreeRTOS. Since, the SAS token expires every 60 minutes, I want to enable refreshing of the token, but I have no clue on what the variable pxTokenRefresh is. It would be great if you can help me understand the what this format of variable declaration means and how do I initialize it.