feat: add support for exporting metrics

[rhamzeh]

Description

Introduces OpenTelemetry metrics reporting into the SDK for specific actions. We're intentionally starting with only a few metric events that we can then grow over time.

We don't have any formal documentation for this currently. We'll write this as we roll it out across all SDKs, so here is a summary of the events and the associated attributes:

Supported Metrics

Metric Name	Type	Description
fga-client.request.duration	Histogram	The total request time for FGA requests
fga-client.query.duration	Histogram	The amount of time the FGA server took to internally process nd evaluate the request
fga-client.credentials.request	Counter	The total number of times a new token was requested when using ClientCredentials

Supported attributes

Attribute Name	Type	Description
fga-client.response.model_id	string	The authorization model ID that the FGA server used
fga-client.request.method	string	The FGA method/action that was performed (e.g. Check, ListObjects, ...) in TitleCase
fga-client.request.store_id	string	The store ID that was sent as part of the request
fga-client.request.model_id	string	The authorization model ID that was sent as part of the request, if any
fga-client.request.client_id	string	The client ID associated with the request, if any
fga-client.user	string	The user that is associated with the action of the request for check and list objects
http.request.resend_count	int	The number of retries attempted (Only sent if the request was retried. Count of 1 means the request was retried once in addition to the original request)
http.response.status_code	int	The status code of the response
http.request.method	string	The HTTP method for the request
http.host	string	Host identifier of the origin the request was sent to
url.scheme	string	HTTP Scheme of the request (http/https)
url.full	string	Full URL of the request
user_agent.original	string	User Agent used in the query
http.client.request.duration	int	The total request time for FGA requests
http.server.request.duration	int	The amount of time the FGA server took to internally process nd evaluate the request

Testing

Spin up Prometheus, build the project and then run the OpenTelemetryExample app.

You should see metrics in Prometheus such as:

fga_client_query_duration_bucket{exported_instance="28790af8-2116-4e47-baaf-319f9f23f518", exported_job=""openfga-otel-dotnet-example"", fga_client_request_client_id="3DSvMhkJwjoSBMTliPEdPjybbVewfVes", fga_client_request_method="Check", fga_client_request_model_id="01J41WCA3KBA9SP2M350FPDEJ0", fga_client_request_store_id="01J40DW2J9NNYNNVEC430S3Z97", fga_client_response_model_id="01J41WCA3KBA9SP2M350FPDEJ0", fga_client_user="user:anne", http_client_request_duration="40", http_host="api.us1.fga.dev", http_request_method="POST", http_response_status_code="200", http_server_request_duration="2", instance="otel-collector:8889", job="otel-collector", label1="value1", le="5", url_full="https://api.us1.fga.dev/stores/01J40DW2J9NNYNNVEC430S3Z97/check", url_scheme="https", user_agent_original="openfga-sdk dotnet/0.4.0"}
---
fga_client_query_duration_bucket{exported_instance="fbee572d-0bff-4957-95a2-c532fe7312c1", exported_job=""openfga-otel-dotnet-example"", fga_client_request_client_id="3DSvMhkJwjoSBMTliPEdPjybbVewfVes", fga_client_request_method="WriteAuthorizationModel", fga_client_request_store_id="01J40DW2J9NNYNNVEC430S3Z97", http_client_request_duration="139", http_host="api.us1.fga.dev", http_request_method="POST", http_request_resend_count="1", http_response_status_code="201", http_server_request_duration="69", instance="otel-collector:8889", job="otel-collector", label1="value1", le="75", url_full="https://api.us1.fga.dev/stores/01J40DW2J9NNYNNVEC430S3Z97/authorization-models", url_scheme="https", user_agent_original="openfga-sdk dotnet/0.4.0"}
---
fga_client_query_duration_bucket{exported_instance="fbee572d-0bff-4957-95a2-c532fe7312c1", exported_job=""openfga-otel-dotnet-example"", fga_client_request_client_id="3DSvMhkJwjoSBMTliPEdPjybbVewfVes", fga_client_request_method="Write", fga_client_request_model_id="01J41WCA3KBA9SP2M350FPDEJ0", fga_client_request_store_id="01J40DW2J9NNYNNVEC430S3Z97", fga_client_response_model_id="01J41WCA3KBA9SP2M350FPDEJ0", http_client_request_duration="68", http_host="api.us1.fga.dev", http_request_method="POST", http_request_resend_count="1", http_response_status_code="200", http_server_request_duration="30", instance="otel-collector:8889", job="otel-collector", label1="value1", le="5000", url_full="https://api.us1.fga.dev/stores/01J40DW2J9NNYNNVEC430S3Z97/write", url_scheme="https", user_agent_original="openfga-sdk dotnet/0.4.0"}

Also for client credential exchange, you should see metrics such as:

{__name__="fga_client_credentials_request", exported_instance="28790af8-2116-4e47-baaf-319f9f23f518", exported_job=""openfga-otel-dotnet-example"", fga_client_request_client_id="3DSvMhkJwjoSBMTliPEdPjybbVewfVes", fga_client_request_method="ClientCredentialsExchange", http_client_request_duration="1461", http_host="fga.us.auth0.com", http_request_method="POST", http_response_status_code="200", instance="otel-collector:8889", job="otel-collector", label1="value1", url_full="https://fga.us.auth0.com/oauth/token", url_scheme="https", user_agent_original="openfga-sdk dotnet/0.4.0"}

References

Closes #68

Follows the implementations in JS (https://github.com/openfga/js-sdk/pull/117), Python (https://github.com/openfga/python-sdk/pull/107) and Java (https://github.com/openfga/java-sdk/pull/94)

Review Checklist

• [x] I have clicked on "allow edits by maintainers".
• [ ] I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• [x] The correct base branch is being used, if not main
• [ ] I have added tests to validate that the change in functionality is working as expected