Allow routingprocessor read value from client.Metadata

[eugene-chernyshenko]

Component(s)

processor/routing

Is your feature request related to a problem? Please describe.

Setting tenant id in server auth extension to route data to correct exporter

Describe the solution you'd like

Is it possible to make routingprocessor take data from client.Metadata too, not only from grpc headers?

This may help for different server auth extensions

Example scenario:

1 In server auth extention we recognize tenant id by token
2 We put it in client.Metadata
3 In routingprocessor we get the required tenant id from client.Metadata by key and send the table data to the required exporter.

Describe alternatives you've considered

No response

Additional context

No response

[github-actions]

Pinging code owners:

• processor/routing: @jpkrohling

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