server: log bcrypt cost if > 12, error on runtime > 10s

The bcrypt hashing algorithm runtime grows exponentially with cost,
and might cause a timeout if the cost is too high. Notifying the user
of high cost and of long running calculations will help with tuning
and debugging.

server/server_test.go

@@ -896,6 +896,116 @@ func TestPasswordDB(t *testing.T) {
 
 }
 
+// A warning message should be logged if password-hash comparison takes longer than 10s
+func TestLoginTimeout(t *testing.T) {
+	s := memory.New(logger)
+	conn := newPasswordDB(s)
+
+	pw := "test1"
+
+	tests := []struct {
+		name, email, password string
+		pwHash                []byte
+		wantIdentity          connector.Identity
+		wantInvalid           bool
+		wantedErr             string
+	}{
+		{
+			name:     "valid password min cost",
+			email:    "jane@example.com",
+			password: pw,
+			// bcrypt hash of the value "test1" with cost 4
+			pwHash: []byte("$2a$04$lGqOe5gnlpsfreQ1OJHxGOO7f5FyyESyICkswSFATM1cnBVgCyyuG"),
+			wantIdentity: connector.Identity{
+				Email:         "jane@example.com",
+				Username:      "jane",
+				UserID:        "foobar",
+				EmailVerified: true,
+			},
+		},
+		{
+			name:     "valid password reccomended cost",
+			email:    "jane@example.com",
+			password: pw,
+			// bcrypt hash of the value "test1" with cost 12
+			pwHash: []byte("$2a$12$VZNNjuCUGX2NG5S1ci.3Ku9mI9DmA9XeXyrr7YzJuyTxuVBGdRAbm"),
+			wantIdentity: connector.Identity{
+				Email:         "jane@example.com",
+				Username:      "jane",
+				UserID:        "foobar",
+				EmailVerified: true,
+			},
+		},
+		{
+			name:     "valid password timeout cost",
+			email:    "jane@example.com",
+			password: pw,
+			// bcrypt hash of the value "test1" with cost 20
+			pwHash:    []byte("$2a$20$yODn5quqK9MZdePqYLs6Y.Jr4cOO1P0aXsKz0eTa2rxOmu8e7ETpi"),
+			wantedErr: fmt.Sprintf("password-hash comparison timeout: your bcrypt cost = 20, recommended cost = %d", recCost),
+		},
+		{
+			name:     "invalid password min cost",
+			email:    "jane@example.com",
+			password: pw,
+			// bcrypt hash of the value "test2" with cost 4
+			pwHash:      []byte("$2a$04$pX8wwwpxw8xlXrToYaEgZemK0JIibMZYXPsgau7aPDoGyHPF73br."),
+			wantInvalid: true,
+		},
+		{
+			name:     "invalid password timeout cost",
+			email:    "jane@example.com",
+			password: pw,
+			// bcrypt hash of the value "test2" with cost 20
+			pwHash:    []byte("$2a$20$WBD9cs63Zf0zqS99yyrQhODoDXphWw8MlYqVYRiftJH.lRJ1stnAa"),
+			wantedErr: fmt.Sprintf("password-hash comparison timeout: your bcrypt cost = 20, recommended cost = %d", recCost),
+		},
+	}
+
+	sEmail, sUsername, sUserID := "jane@example.com", "jane", "foobar"
+	for _, tc := range tests {
+		// Clean up before new test case
+		s.DeletePassword(sEmail)
+
+		s.CreatePassword(storage.Password{
+			Email:    sEmail,
+			Username: sUsername,
+			UserID:   sUserID,
+			Hash:     tc.pwHash,
+		})
+
+		ident, valid, err := conn.Login(context.Background(), connector.Scopes{}, tc.email, tc.password)
+		if err != nil {
+			if err.Error() != tc.wantedErr {
+				t.Errorf("%s: error was incorrect:\n%v", tc.name, err)
+			}
+			continue
+		}
+
+		if tc.wantedErr != "" {
+			t.Errorf("%s: expected error", tc.name)
+			continue
+		}
+
+		if !valid {
+			if !tc.wantInvalid {
+				t.Errorf("%s: expected valid response", tc.name)
+			}
+			continue
+		}
+
+		if tc.wantInvalid {
+			t.Errorf("%s: expected invalid response", tc.name)
+			continue
+		}
+
+		if diff := pretty.Compare(tc.wantIdentity, ident); diff != "" {
+			t.Errorf("%s: %s", tc.email, diff)
+		}
+	}
+
+}
+
 type storageWithKeysTrigger struct {
 	storage.Storage
 	f func()