OAuth M2M: token requests ignore the connector's User-Agent (WithUserAgentEntry not threaded into the token exchange)

首先阅读 auth/oauth/m2m/m2m.go 和 internal/client/client.go，重点关注用于创建 token source 的 context，以及应用 BuildUserAgent 的位置。跟踪 connector 的 OAuth M2M 路径，并验证 token 请求使用配置的 User-Agent，同时检查 auth/oauth/oauth.go 中另行指出的 endpoint 解析限制。完成的标准是，mintOAuthToken 审计条目能够识别配置的 connector，而不是 Go 的默认 client。

Summary

When a connector authenticates with OAuth M2M (WithClientCredentials, or client credentials via DSN), the driver's token requests are issued with Go's default HTTP client, so they reach the workspace as Go-http-client/2.0 instead of the User-Agent configured through WithUserAgentEntry. Query traffic is attributed correctly — only the token exchange is anonymous.

This matters for ISV partner attribution: the Databricks partner program asks integrations to identify themselves via a programmatic User-Agent, and these token grants show up in system.access.audit as an unidentified generic Go client.

Current behavior

Connector configured as:

connector, err := dbsql.NewConnector(
    dbsql.WithServerHostname(host),
    dbsql.WithPort(443),
    dbsql.WithHTTPPath(httpPath),
    dbsql.WithClientCredentials(clientID, clientSecret),
    dbsql.WithUserAgentEntry("MyISV_MyProduct/1.0"),
)

system.access.audit rows for the resulting activity (identifiers redacted):

service_name	action_name	user_agent
workspace	workspaceInHouseOAuthClientAuthentication	Go-http-client/2.0
workspace	mintOAuthToken	Go-http-client/2.0
accounts	oidcTokenAuthorization	godatabrickssqlconnector/1.13.0 (MyISV_MyProduct/1.0)

The Thrift/query path carries the configured entry as expected; the token-mint requests do not.

Root cause

BuildUserAgent(cfg) is applied only to the Thrift HTTP client:

• internal/client/client.go — thriftHttpClient.SetHeader("User-Agent", BuildUserAgent(cfg))

The M2M authenticator builds its token source with a hardcoded background context, so a caller has no way to supply an *http.Client — oauth2 takes its HTTP client from the context (oauth2.HTTPClient), and that context never leaves the package:

• auth/oauth/m2m/m2m.go (on main) — GetConfig(context.Background(), ...) and config.TokenSource(context.Background())

Because of that, neither WithUserAgentEntry nor WithTransport can influence token requests.

This is adjacent to a limitation already acknowledged in-tree for the endpoint-resolution path (auth/oauth/oauth.go):

NOTE: this client uses the default transport, matching the existing oidc.NewProvider discovery below. A connector-supplied transport / TLS config (WithTransport, WithSkipTLSHostVerify) is not yet threaded into the OAuth endpoint-resolution path; that is a pre-existing limitation, tracked separately.

This report is that same limitation one step further along: the token exchange itself.

Expected behavior

Token requests (and ideally OIDC discovery) carry the same User-Agent as the rest of the connector's traffic — which is what BuildUserAgent's own doc comment states as the intent:

…used by the driver for Thrift, telemetry, and feature-flag requests so all traffic from a single connection is attributable to the same identifier in access logs.

Possible directions

1. Thread the connector's HTTP client/context into the authenticator — e.g. have the connector pass an *http.Client built with the driver's transport + User-Agent, and create the token source with context.WithValue(ctx, oauth2.HTTPClient, client).
2. Or expose an option to supply the token-exchange HTTP client, so callers can set headers without re-implementing the M2M flow.

We verified direction 1 works: injecting an *http.Client whose RoundTripper sets the User-Agent into the token source makes every mintOAuthToken audit row correctly attributed. We did not keep that as a workaround — replacing the built-in authenticator with an application-side copy of the credential flow would risk drifting from upstream on every release, which is exactly why we'd prefer this handled in the driver.

Environment

• databricks-sql-go v1.13.0 — code path verified unchanged in v1.14.0 and on main
• Auth: OAuth M2M (client credentials, Databricks-managed service principal)
• Go 1.25, Linux

Happy to open a PR for direction 1 if you'd like it contributed.