fix(auth): allow customizing top app bar colors via AuthUITheme

[demolaf]

Fixes #2390.

AuthUITheme.topAppBarColors was a companion-object getter derived from the ambient MaterialTheme.colorScheme, so there was no way to override it per AuthUITheme instance — apps couldn't align the auth screens' top app bar with their own branding.

Usage

val customTheme = AuthUITheme.Default.copy(
    topAppBarColors = TopAppBarColors(
        containerColor = Color(0xFFFFA000), // firebase primary color - amber
        scrolledContainerColor = Color(0xFFFFA000),
        navigationIconContentColor = Color.White,
        titleContentColor = Color.White,
        actionIconContentColor = Color.White,
        subtitleContentColor = Color.White,
    )
)

val configuration = authUIConfiguration {
    context = applicationContext
    theme = customTheme
    // ...
}

Preview

[gemini-code-assist]

Code Review

This pull request introduces the ability to customize top app bar colors on authentication screens by adding a topAppBarColors property to AuthUITheme and applying it across various UI screens. The review feedback highlights a compilation error in HighLevelApiDemoActivity.kt due to the use of a non-existent subtitleContentColor parameter in Material 3's TopAppBarColors. Additionally, because TopAppBarColors is an experimental API, the reviewer recommends adding the @OptIn(ExperimentalMaterial3Api::class) annotation locally in the demo activity and propagating the @property:ExperimentalMaterial3Api annotation to the public property in AuthUITheme.

[russellwheatley]

A few bits of feedback

SelectFactorUI's TopAppBar in MfaEnrollmentDefaults.kt doesn't take colors at all, so it won't pick up topAppBarColors (or even the existing default). Can you wire that one up too, otherwise the 2FA screen won't match once someone sets a custom color.

see auth/src/main/java/com/firebase/ui/auth/ui/screens/MfaEnrollmentDefaults.kt:255 (the TopAppBar call inside SelectFactorUI)

[russellwheatley]

A few bits of feedback

topAppBarColors on AuthUITheme (and the matching copy() param) is typed as TopAppBarColors, which is still @ExperimentalMaterial3Api, but neither is annotated. Anyone who actually sets it - the whole point of this PR -gets a compile error with no hint why unless they already have @OptIn in scope elsewhere. Can you propagate the opt-in onto the property and the copy() param?

see auth/src/main/java/com/firebase/ui/auth/configuration/theme/AuthUITheme.kt:90 and :110

Same issue bites the demo itself — TopAppBarColors(...) is constructed inside onCreate/setContent, but the only @OptIn(ExperimentalMaterial3Api::class) in the file is on the unrelated composable further down. As it stands this won't compile.

see app/src/main/java/com/firebaseui/android/demo/HighLevelApiDemoActivity.kt:88 (missing @OptIn on onCreate, existing one is at line 252)

Nit: README and demo both construct TopAppBarColors(...) with all six params instead of going through TopAppBarDefaults.topAppBarColors(...) like the rest of the codebase does (including our own default at AuthUITheme.kt:247). Worth switching for consistency and so we don't break if Material3 adds params later.

[demolaf]

topAppBarColors on AuthUITheme (and the matching copy() param) is typed as TopAppBarColors, which is still @ExperimentalMaterial3Api, but neither is annotated. Anyone who actually sets it - the whole point of this PR -gets a compile error with no hint why unless they already have @OptIn in scope elsewhere. Can you propagate the opt-in onto the property and the copy() param?

I think it compiles fine. In newer versions of compose bom the APIs are now stable, before the compose bom was updated this (i.e. @OptIn(ExperimentalMaterial3Api::class)) was needed but i've taken it out now.

[demolaf]

Nit: README and demo both construct TopAppBarColors(...) with all six params instead of going through TopAppBarDefaults.topAppBarColors(...) like the rest of the codebase does (including our own default at AuthUITheme.kt:247). Worth switching for consistency and so we don't break if Material3 adds params later.

Valid point, i'll make the necessary changes to the demo and README.

[demolaf]

@russellwheatley anything else blocking this from being merged?

[russellwheatley]

@demolaf - just the merge conflict and I think we're good to go 👍