Propagate correct `User-Agent` for CLI (#1264)

## Changes
This PR migrates `databricks auth login` HTTP client to the one from Go
SDK, making API calls more robust and containing our unified user agent.

## Tests
Unit tests left almost unchanged

libs/auth/oauth.go

@@ -6,16 +6,14 @@ import (
 	"crypto/sha256"
 	_ "embed"
 	"encoding/base64"
-	"encoding/json"
 	"errors"
 	"fmt"
-	"io"
 	"net"
-	"net/http"
 	"strings"
 	"time"
 
 	"github.com/databricks/cli/libs/auth/cache"
+	"github.com/databricks/databricks-sdk-go/httpclient"
 	"github.com/databricks/databricks-sdk-go/retries"
 	"github.com/pkg/browser"
 	"golang.org/x/oauth2"
@@ -43,16 +41,12 @@ type PersistentAuth struct {
 	Host      string
 	AccountID string
 
-	http    httpGet
+	http    *httpclient.ApiClient
 	cache   tokenCache
 	ln      net.Listener
 	browser func(string) error
 }
 
-type httpGet interface {
-	Get(string) (*http.Response, error)
-}
-
 type tokenCache interface {
 	Store(key string, t *oauth2.Token) error
 	Lookup(key string) (*oauth2.Token, error)
@@ -77,10 +71,12 @@ func (a *PersistentAuth) Load(ctx context.Context) (*oauth2.Token, error) {
 	}
 	// OAuth2 config is invoked only for expired tokens to speed up
 	// the happy path in the token retrieval
-	cfg, err := a.oauth2Config()
+	cfg, err := a.oauth2Config(ctx)
 	if err != nil {
 		return nil, err
 	}
+	// make OAuth2 library use our client
+	ctx = a.http.InContextForOAuth2(ctx)
 	// eagerly refresh token
 	refreshed, err := cfg.TokenSource(ctx, t).Token()
 	if err != nil {
@@ -110,7 +106,7 @@ func (a *PersistentAuth) Challenge(ctx context.Context) error {
 	if err != nil {
 		return fmt.Errorf("init: %w", err)
 	}
-	cfg, err := a.oauth2Config()
+	cfg, err := a.oauth2Config(ctx)
 	if err != nil {
 		return err
 	}
@@ -120,6 +116,8 @@ func (a *PersistentAuth) Challenge(ctx context.Context) error {
 	}
 	defer cb.Close()
 	state, pkce := a.stateAndPKCE()
+	// make OAuth2 library use our client
+	ctx = a.http.InContextForOAuth2(ctx)
 	ts := authhandler.TokenSourceWithPKCE(ctx, cfg, state, cb.Handler, pkce)
 	t, err := ts.Token()
 	if err != nil {
@@ -138,7 +136,9 @@ func (a *PersistentAuth) init(ctx context.Context) error {
 		return ErrFetchCredentials
 	}
 	if a.http == nil {
-		a.http = http.DefaultClient
+		a.http = httpclient.NewApiClient(httpclient.ClientConfig{
+			// noop
+		})
 	}
 	if a.cache == nil {
 		a.cache = &cache.TokenCache{}
@@ -172,7 +172,7 @@ func (a *PersistentAuth) Close() error {
 	return a.ln.Close()
 }
 
-func (a *PersistentAuth) oidcEndpoints() (*oauthAuthorizationServer, error) {
+func (a *PersistentAuth) oidcEndpoints(ctx context.Context) (*oauthAuthorizationServer, error) {
 	prefix := a.key()
 	if a.AccountID != "" {
 		return &oauthAuthorizationServer{
@@ -180,31 +180,20 @@ func (a *PersistentAuth) oidcEndpoints() (*oauthAuthorizationServer, error) {
 			TokenEndpoint:         fmt.Sprintf("%s/v1/token", prefix),
 		}, nil
 	}
+	var oauthEndpoints oauthAuthorizationServer
 	oidc := fmt.Sprintf("%s/oidc/.well-known/oauth-authorization-server", prefix)
-	oidcResponse, err := a.http.Get(oidc)
+	err := a.http.Do(ctx, "GET", oidc, httpclient.WithResponseUnmarshal(&oauthEndpoints))
 	if err != nil {
 		return nil, fmt.Errorf("fetch .well-known: %w", err)
 	}
-	if oidcResponse.StatusCode != 200 {
+	var httpErr *httpclient.HttpError
+	if errors.As(err, &httpErr) && httpErr.StatusCode != 200 {
 		return nil, ErrOAuthNotSupported
 	}
-	if oidcResponse.Body == nil {
-		return nil, fmt.Errorf("fetch .well-known: empty body")
-	}
-	defer oidcResponse.Body.Close()
-	raw, err := io.ReadAll(oidcResponse.Body)
-	if err != nil {
-		return nil, fmt.Errorf("read .well-known: %w", err)
-	}
-	var oauthEndpoints oauthAuthorizationServer
-	err = json.Unmarshal(raw, &oauthEndpoints)
-	if err != nil {
-		return nil, fmt.Errorf("parse .well-known: %w", err)
-	}
 	return &oauthEndpoints, nil
 }
 
-func (a *PersistentAuth) oauth2Config() (*oauth2.Config, error) {
+func (a *PersistentAuth) oauth2Config(ctx context.Context) (*oauth2.Config, error) {
 	// in this iteration of CLI, we're using all scopes by default,
 	// because tools like CLI and Terraform do use all apis. This
 	// decision may be reconsidered later, once we have a proper
@@ -213,7 +202,7 @@ func (a *PersistentAuth) oauth2Config() (*oauth2.Config, error) {
 		"offline_access",
 		"all-apis",
 	}
-	endpoints, err := a.oidcEndpoints()
+	endpoints, err := a.oidcEndpoints(ctx)
 	if err != nil {
 		return nil, fmt.Errorf("oidc: %w", err)
 	}

libs/auth/oauth_test.go

@@ -5,14 +5,14 @@ import (
 	"crypto/tls"
 	_ "embed"
 	"fmt"
-	"io"
 	"net/http"
 	"net/url"
-	"strings"
 	"testing"
 	"time"
 
 	"github.com/databricks/databricks-sdk-go/client"
+	"github.com/databricks/databricks-sdk-go/httpclient"
+	"github.com/databricks/databricks-sdk-go/httpclient/fixtures"
 	"github.com/databricks/databricks-sdk-go/qa"
 	"github.com/stretchr/testify/assert"
 	"golang.org/x/oauth2"
@@ -24,34 +24,29 @@ func TestOidcEndpointsForAccounts(t *testing.T) {
 		AccountID: "xyz",
 	}
 	defer p.Close()
-	s, err := p.oidcEndpoints()
+	s, err := p.oidcEndpoints(context.Background())
 	assert.NoError(t, err)
 	assert.Equal(t, "https://abc/oidc/accounts/xyz/v1/authorize", s.AuthorizationEndpoint)
 	assert.Equal(t, "https://abc/oidc/accounts/xyz/v1/token", s.TokenEndpoint)
 }
 
-type mockGet func(url string) (*http.Response, error)
-
-func (m mockGet) Get(url string) (*http.Response, error) {
-	return m(url)
-}
-
 func TestOidcForWorkspace(t *testing.T) {
 	p := &PersistentAuth{
 		Host: "abc",
-		http: mockGet(func(url string) (*http.Response, error) {
-			assert.Equal(t, "https://abc/oidc/.well-known/oauth-authorization-server", url)
-			return &http.Response{
-				StatusCode: 200,
-				Body: io.NopCloser(strings.NewReader(`{
+		http: httpclient.NewApiClient(httpclient.ClientConfig{
+			Transport: fixtures.MappingTransport{
+				"GET /oidc/.well-known/oauth-authorization-server": {
+					Status: 200,
+					Response: map[string]string{
 						"authorization_endpoint": "a",
-					"token_endpoint": "b"
-				}`)),
-			}, nil
+						"token_endpoint":         "b",
+					},
+				},
+			},
 		}),
 	}
 	defer p.Close()
-	endpoints, err := p.oidcEndpoints()
+	endpoints, err := p.oidcEndpoints(context.Background())
 	assert.NoError(t, err)
 	assert.Equal(t, "a", endpoints.AuthorizationEndpoint)
 	assert.Equal(t, "b", endpoints.TokenEndpoint)