chore: refactor codersdk to use SessionTokenProvider (#19565)

Refactors `codersdk.Client`'s use of session tokens to use a `SessionTokenProvider`, which abstracts the obtaining and storing of the session token.

The main motiviation is to unify Agent authentication an an upstack PR, which can use cloud instance identity via token exchange, rather than a fixed session token.

However, the abstraction could also allow functionality like obtaining the session token from other external sources like the OS credential manager, or an external secret/key management system like Vault.

cli/exp_task_status_test.go

@@ -243,13 +243,12 @@ STATE CHANGED  STATUS   STATE  MESSAGE
 				ctx    = testutil.Context(t, testutil.WaitShort)
 				now    = time.Now().UTC() // TODO: replace with quartz
 				srv    = httptest.NewServer(http.HandlerFunc(tc.hf(ctx, now)))
-				client = new(codersdk.Client)
+				client = codersdk.New(testutil.MustURL(t, srv.URL))
 				sb     = strings.Builder{}
 				args   = []string{"exp", "task", "status", "--watch-interval", testutil.IntervalFast.String()}
 			)
 
 			t.Cleanup(srv.Close)
-			client.URL = testutil.MustURL(t, srv.URL)
 			args = append(args, tc.args...)
 			inv, root := clitest.New(t, args...)
 			inv.Stdout = &sb

cli/exp_taskcreate_test.go

@@ -5,14 +5,12 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
-	"net/url"
 	"strings"
 	"testing"
 	"time"
 
 	"github.com/google/uuid"
 	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 
 	"github.com/coder/coder/v2/cli/clitest"
 	"github.com/coder/coder/v2/cli/cliui"
@@ -236,7 +234,7 @@ func TestTaskCreate(t *testing.T) {
 			var (
 				ctx    = testutil.Context(t, testutil.WaitShort)
 				srv    = httptest.NewServer(tt.handler(t, ctx))
-				client = new(codersdk.Client)
+				client = codersdk.New(testutil.MustURL(t, srv.URL))
 				args   = []string{"exp", "task", "create"}
 				sb     strings.Builder
 				err    error
@@ -244,9 +242,6 @@ func TestTaskCreate(t *testing.T) {
 
 			t.Cleanup(srv.Close)
 
-			client.URL, err = url.Parse(srv.URL)
-			require.NoError(t, err)
-
 			inv, root := clitest.New(t, append(args, tt.args...)...)
 			inv.Environ = serpent.ParseEnviron(tt.env, "")
 			inv.Stdout = &sb

cli/root.go

@@ -635,6 +635,9 @@ func (r *RootCmd) HeaderTransport(ctx context.Context, serverURL *url.URL) (*cod
 }
 
 func (r *RootCmd) configureClient(ctx context.Context, client *codersdk.Client, serverURL *url.URL, inv *serpent.Invocation) error {
+	if client.SessionTokenProvider == nil {
+		client.SessionTokenProvider = codersdk.FixedSessionTokenProvider{}
+	}
 	transport := http.DefaultTransport
 	transport = wrapTransportWithTelemetryHeader(transport, inv)
 	if !r.noVersionCheck {