fix: tune clock drift for slow-mono case

Signed-off-by: Babak K. Shandiz <babakks@github.com>

Author: babakks

device/device_flow.go

@@ -257,7 +257,7 @@ func Wait(ctx context.Context, c httpClient, uri string, opts WaitOptions) (*api
 			// should not cause slow_down errors, unless the slow monotonic clock
 			// is still ticking faster than the OAuth server's clock. For such
 			// cases we tolerate a few more slow-downs.
-			if slowDowns > 2 && driftRatio > 0.05 || slowDowns > 4 && driftRatio < 0 {
+			if slowDowns > 2 && driftRatio > 0.05 || slowDowns > 4 && driftRatio < -0.05 {
 				return nil, fmt.Errorf("received too many slow_down responses; detected clock drift of roughly %.0f%% between monotonic and wall clocks; please ensure your system clock is accurate", driftRatio*100)
 			}
 

device/device_flow_test.go

@@ -707,7 +707,7 @@ func TestPollToken(t *testing.T) {
 			},
 		},
 		{
-			name: "failure with multiple slow downs, due to high clock drift (mono slower)",
+			name: "failure with multiple slow downs, due to high clock drift (mono faster)",
 			args: args{
 				http: apiClient{
 					stubs: []apiStub{
@@ -815,10 +815,10 @@ func TestPollToken(t *testing.T) {
 						Interval:        5,
 					},
 					newPoller:                singletonFakePoller(6),
-					calculateTimeDriftRatioF: newCalculateTimeDriftRatioStub(-0.01, -0.01, -0.01, -0.01, -0.01),
+					calculateTimeDriftRatioF: newCalculateTimeDriftRatioStub(-0.051, -0.051, -0.051, -0.051, -0.051),
 				},
 			},
-			wantErr: `received too many slow_down responses; detected clock drift of roughly -1% between monotonic and wall clocks; please ensure your system clock is accurate`,
+			wantErr: `received too many slow_down responses; detected clock drift of roughly -5% between monotonic and wall clocks; please ensure your system clock is accurate`,
 			posts: repeatPostArgs(6, postArgs{
 				url: "https://github.com/oauth",
 				params: url.Values{