Set the Key based on the file data of collection message

Working with Data Connectors & Integrations
1

Hi Team/@Ross_Lawley ,

I need to set the topic Key value from the mongoDB collection field(user_guid) in string formate. I saw the document MongoDB Connector for Apache Kafka 1.3 Available Now | MongoDB Blog
But here Key has set with the help of AVRO schema, Does there any way exists to set it on string bases. Please check below give source connecter config and let me know how can i set user_guid value as the value of Key in topic.

My current config:

{
  "name": "MongoSourceConnectorConnector_2",
  "config": {
    "value.converter.schema.registry.url": "http://schema-registry:8081",
    "name": "MongoSourceConnectorConnector_2",
    "connector.class": "com.mongodb.kafka.connect.MongoSourceConnector",
    "tasks.max": "1",
    "value.converter": "io.confluent.connect.avro.AvroConverter",
    "errors.tolerance": "none",
    "errors.log.enable": "true",
    "connection.uri": "***",
    "database": "Test",
    "collection": "user_product_items",
    "pipeline": "[ {$match:      {\"operationType\": { $in : [\"insert\", \"update\"]}} }]",
    "publish.full.document.only": "true",
    "poll.max.batch.size": "1000",
    "poll.await.time.ms": "5000",
    "topic.namespace.map": "{\"Test.user_product_items\":\"user_product_items27\"}",
    "output.format.value": "schema",
    "output.schema.infer.value": "false",
    "output.schema.value": "{   \"name\": \"user_product_items\",   \"connect.name\": \"user_product_items\",   \"namespace\": \"Icis.Subscription\",   \"type\": \"record\",   \"fields\": [     {       \"name\": \"metadata\",       \"type\": {         \"name\": \"metadata\",         \"type\": \"record\",         \"fields\": [           {             \"name\": \"event_type\",             \"type\": \"string\"           },           {             \"name\": \"partition_key\",             \"type\": \"string\"           },           {             \"name\": \"correlation_id\",             \"type\": \"string\"           },           {             \"name\": \"id\",             \"type\": \"string\"           },           {             \"name\": \"source\",             \"type\": \"string\"           },           {             \"name\": \"type\",             \"type\": \"string\"           },           {             \"name\": \"event_time\",             \"type\": \"string\"           },           {             \"name\": \"released_on\",             \"type\": \"string\"           }         ]       }     },     {       \"name\": \"user_identity_id\",       \"type\": \"int\"     },     {       \"name\": \"user_guid\",       \"type\": \"string\"     },     {       \"name\": \"status\",       \"type\": \"string\"     },     {       \"name\": \"last_updated_on\",       \"type\": \"long\"     },     {       \"name\": \"product_items\",       \"type\": {         \"type\": \"array\",         \"items\": \"string\"       }     }   ] }",
    "mongo.errors.tolerance": "all",
    "mongo.errors.log.enable": "true",
    "offset.partition.name": "user_prefrence_partition9"
  }
}

Expected key like:
image