feat: AuthUITheme, ProviderStyle and tests (#2224)

- added junit ui test library for compose ui tests
- refactor: default provider styles
- test: integration tests to validate AuthUITheme.Default is injected by default
- test: validate fromMaterialTheme inherits clients MaterialTheme when AuthUITheme overridden

Author: demolaf

auth/build.gradle.kts

@@ -115,6 +115,7 @@ dependencies {
     testImplementation(Config.Libs.Test.robolectric)
     testImplementation(Config.Libs.Test.kotlinReflect)
     testImplementation(Config.Libs.Provider.facebook)
+    testImplementation(libs.androidx.ui.test.junit4)
 
     debugImplementation(project(":internal:lintchecks"))
 }

auth/src/main/java/com/firebase/ui/auth/compose/configuration/AuthUIConfiguration.kt

@@ -20,6 +20,7 @@ import com.google.firebase.auth.ActionCodeSettings
 import androidx.compose.ui.graphics.vector.ImageVector
 import com.firebase.ui.auth.compose.configuration.stringprovider.AuthUIStringProvider
 import com.firebase.ui.auth.compose.configuration.stringprovider.DefaultAuthUIStringProvider
+import com.firebase.ui.auth.compose.configuration.theme.AuthUITheme
 
 fun actionCodeSettings(block: ActionCodeSettings.Builder.() -> Unit) =
     ActionCodeSettings.newBuilder().apply(block).build()

auth/src/main/java/com/firebase/ui/auth/compose/configuration/AuthUITheme.kt

@@ -0,0 +1,130 @@
+/*
+ * Copyright 2025 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.firebase.ui.auth.compose.configuration.theme
+
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material3.ColorScheme
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Shapes
+import androidx.compose.material3.Typography
+import androidx.compose.material3.lightColorScheme
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.Shape
+import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.dp
+
+/**
+ * Theming configuration for the entire Auth UI.
+ */
+class AuthUITheme(
+    /**
+     * The color scheme to use.
+     */
+    val colorScheme: ColorScheme,
+
+    /**
+     * The typography to use.
+     */
+    val typography: Typography,
+
+    /**
+     * The shapes to use for UI elements.
+     */
+    val shapes: Shapes,
+
+    /**
+     * A map of provider IDs to custom styling.
+     */
+    val providerStyles: Map<String, ProviderStyle> = emptyMap()
+) {
+
+    /**
+     * A class nested within AuthUITheme that defines the visual appearance of a specific
+     * provider button, allowing for per-provider branding and customization.
+     */
+    class ProviderStyle(
+        /**
+         * The background color of the button.
+         */
+        val backgroundColor: Color,
+
+        /**
+         * The color of the text label on the button.
+         */
+        val contentColor: Color,
+
+        /**
+         * An optional tint color for the provider's icon. If null,
+         * the icon's intrinsic color is used.
+         */
+        var iconTint: Color? = null,
+
+        /**
+         * The shape of the button container. Defaults to RoundedCornerShape(4.dp).
+         */
+        val shape: Shape = RoundedCornerShape(4.dp),
+
+        /**
+         * The shadow elevation for the button. Defaults to 2.dp.
+         */
+        val elevation: Dp = 2.dp
+    )
+
+    companion object {
+        /**
+         * A standard light theme with Material 3 defaults and
+         * pre-configured provider styles.
+         */
+        val Default = AuthUITheme(
+            colorScheme = lightColorScheme(
+                primary = Color(0xFFFFA611)
+            ),
+            typography = Typography(),
+            shapes = Shapes(),
+            providerStyles = ProviderStyleDefaults.default
+        )
+
+        /**
+         * Creates a theme inheriting the app's current Material
+         * Theme settings.
+         */
+        @Composable
+        fun fromMaterialTheme(
+            providerStyles: Map<String, ProviderStyle> = ProviderStyleDefaults.default
+        ): AuthUITheme {
+            return AuthUITheme(
+                colorScheme = MaterialTheme.colorScheme,
+                typography = MaterialTheme.typography,
+                shapes = MaterialTheme.shapes,
+                providerStyles = providerStyles
+            )
+        }
+
+    }
+}
+
+@Composable
+fun AuthUITheme(
+    theme: AuthUITheme = AuthUITheme.Default,
+    content: @Composable () -> Unit
+) {
+    MaterialTheme(
+        colorScheme = theme.colorScheme,
+        typography = theme.typography,
+        shapes = theme.shapes,
+        content = content
+    )
+}