Salesforce: Get record ID from a DataSourceConnection class - salesforce

Question

I have a Custom DataSourceConnection class (that extends DataSource.Connection) to retrieve related records for contacts from my server API. I need the record ID for the current contact to make my query, but haven't found a way to retrieve it (ApexPages won't work because it's not using Visualforce).
How can I get the record ID from my DataSourceConnection class?
EDIT:
Here are more details on my issue:
The class is being used/called by an External Object that uses a External Data Source, which uses my Custom DataSourceProvider + DataSourceConnection. It's based on this article:
https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_connector_start.htm
I need to get the record ID in the "SampleDataSourceConnection" class, inside the "getRows" method that is called by the overrided "query" method. This is how the code looks:
global class SampleDataSourceConnection
extends DataSource.Connection {
global SampleDataSourceConnection(DataSource.ConnectionParams
connectionParams) {
}
// ...
// ...
override global DataSource.TableResult query(
DataSource.QueryContext context) {
if (context.tableSelection.columnsSelected.size() == 1 &&
context.tableSelection.columnsSelected.get(0).aggregation ==
DataSource.QueryAggregation.COUNT) {
List<Map<String,Object>> rows = getRows(context);
List<Map<String,Object>> response =
DataSource.QueryUtils.filter(context, getRows(context));
List<Map<String, Object>> countResponse =
new List<Map<String, Object>>();
Map<String, Object> countRow =
new Map<String, Object>();
countRow.put(
context.tableSelection.columnsSelected.get(0).columnName,
response.size());
countResponse.add(countRow);
return DataSource.TableResult.get(context,
countResponse);
} else {
List<Map<String,Object>> filteredRows =
DataSource.QueryUtils.filter(context, getRows(context));
List<Map<String,Object>> sortedRows =
DataSource.QueryUtils.sort(context, filteredRows);
List<Map<String,Object>> limitedRows =
DataSource.QueryUtils.applyLimitAndOffset(context,
sortedRows);
return DataSource.TableResult.get(context, limitedRows);
}
}
// ...
// ...
// Helper method to get record values from the external system for the Sample table.
private List<Map<String, Object>> getRows () {
// Get row field values for the Sample table from the external system via a callout.
HttpResponse response = makeGetCallout();
// Parse the JSON response and populate the rows.
Map<String, Object> m = (Map<String, Object>)JSON.deserializeUntyped(
response.getBody());
Map<String, Object> error = (Map<String, Object>)m.get('error');
if (error != null) {
throwException(string.valueOf(error.get('message')));
}
List<Map<String,Object>> rows = new List<Map<String,Object>>();
List<Object> jsonRows = (List<Object>)m.get('value');
if (jsonRows == null) {
rows.add(foundRow(m));
} else {
for (Object jsonRow : jsonRows) {
Map<String,Object> row = (Map<String,Object>)jsonRow;
rows.add(foundRow(row));
}
}
return rows;
}
// ...
I understand that the External Object relates to the Contact Object automatically by the ContactId, but I don't have the ContactId on the external system, so I have to grab the contact email (and so the current contact id) to relate it with the external system...