How to implement OpenAPI Dictionary/Map defined with object as key

Hi Team,

3GPP 29.519 (Rel 16) specification has defined a data model which uses object as a map key (snippets below). SmPolicyData object has defined smPolicySnssaiData as a map with Snssai (object) as the key. As per OAS 3.0, key of a Dictionary/Map must be a string and Codegen is generating the map as Map<String, SmPolicyDnnData> as expected. How should the implementation convert the object value to a string when generating JSON? Does OpenAPI define any format to map object to string or is it implementation dependent?

Snippets from 29.519 API specification:

    SmPolicyData:

      description: Contains the SM policy data for a given subscriber.

      type: object

      properties:

        smPolicySnssaiData:

          type: object

          additionalProperties:

            $ref: '#/components/schemas/SmPolicySnssaiData'

          minProperties: 1

        umDataLimits:

          type: object

          additionalProperties:

            $ref: '#/components/schemas/UsageMonDataLimit'

          minProperties: 1

        umData:

          type: object

          additionalProperties:

            $ref: '#/components/schemas/UsageMonData'

          minProperties: 1

        suppFeat:

          $ref: 'TS29571_CommonData.yaml#/components/schemas/SupportedFeatures'

      required:

        - smPolicySnssaiData

    SmPolicySnssaiData:

      description: Contains the SM policy data for a given subscriber and S-NSSAI.

      type: object

      properties:

        snssai:

          $ref: 'TS29571_CommonData.yaml#/components/schemas/Snssai'

        smPolicyDnnData:

          type: object

          additionalProperties:

            $ref: '#/components/schemas/SmPolicyDnnData'

          minProperties: 1

      required:

        - snssai

Snippet from 29.571 API specification:

    Snssai:

      type: object

      properties:

        sst:

          type: integer

          minimum: 0

          maximum: 255

        sd:

          type: string

          pattern: '^[A-Fa-f0-9]{6}$'

      required:

        - sst

Any help is highly appreciated.

Thanks

Carthic