[demolaf]

Related to #1400.

Adds a full customization example to the SwiftUI sample: every auth screen drawn by the app, with three live-switchable themes from the "Firebase auth flows" Figma file.

Draft: based on #1412 with #1414 to #1417 merged in, so the diff includes them. It gets rebased onto main once #1402 to #1417 merge.

Changes

• .pickerContent { state in } draws the Figma Landing; .pickerDestination and .signedInContent replace every other screen through its content slot.
• Doggo, Grid and Coffee Spark come from the iOS Landing frames. Screens Figma lacks follow the Android demo's copy.
• The theming modifiers restyle the stock screens left in the flow: update password, reauthentication and delete confirmation.
• The example owns its AuthService to enable email-link sign-in without changing other examples. Fonts ship with their OFL licenses.

Preview

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Maintainer note: Fixes internal CPRN-523

[gemini-code-assist]

Code Review

This pull request refactors the authentication views in FirebaseAuthSwiftUI to support full UI customization by introducing customizable screen wrappers (such as EmailAuthScreen and MFAEnrolmentScreen) and extracting the stock UI into default content views. It also adds a comprehensive multi-theme customization example to the sample application. The review feedback highlights critical improvements, including reusing a static CIContext for QR code generation to prevent performance degradation, and replacing a force cast with safe optional casting to avoid potential runtime crashes.

[gemini-code-assist]

Creating a new CIContext on every invocation of generateQRCode(from:) is highly inefficient and can cause UI stuttering/performance degradation because CIContext is expensive to instantiate. It is recommended to reuse a single shared/static CIContext instance.

  private static let qrContext = CIContext()

  private func generateQRCode(from string: String) -> UIImage? {
    let data = Data(string.utf8)

    guard let filter = CIFilter(name: "CIQRCodeGenerator") else { return nil }
    filter.setValue(data, forKey: "inputMessage")
    filter.setValue("H", forKey: "inputCorrectionLevel")

    guard let ciImage = filter.outputImage else { return nil }

    // Scale up the QR code for better quality
    let transform = CGAffineTransform(scaleX: 10, y: 10)
    let scaledImage = ciImage.transformed(by: transform)

    guard let cgImage = Self.qrContext.createCGImage(scaledImage, from: scaledImage.extent) else {
      return nil
    }

    return UIImage(cgImage: cgImage)
  }

[gemini-code-assist]

Force casting factor as! PhoneMultiFactorInfo can lead to runtime crashes if the factor is not of the expected type. It is safer and more idiomatic to use safe optional casting (as?) to prevent potential crashes.

        if let phoneInfo = factor as? PhoneMultiFactorInfo {
          Text("SMS: \(phoneInfo.phoneNumber)")
            .authFont(.caption)
            .foregroundColor(.secondary)
        } else {
          Text("Authenticator App")
            .authFont(.caption)
            .foregroundColor(.secondary)
        }

[gemini-code-assist]

Instantiating a new CIContext inside the initializer of DemoQRCode is inefficient because SwiftUI views are frequently recreated. Reusing a single static CIContext avoids this overhead.

Suggested change

	private struct DemoQRCode: View {
	let image: UIImage
	init?(url: URL) {
	let filter = CIFilter.qrCodeGenerator()
	filter.message = Data(url.absoluteString.utf8)
	guard let output = filter.outputImage?.transformed(by: CGAffineTransform(scaleX: 8, y: 8)),
	let cgImage = CIContext().createCGImage(output, from: output.extent) else {
	return nil
	}
	image = UIImage(cgImage: cgImage)
	}
	private struct DemoQRCode: View {
	private static let qrContext = CIContext()
	let image: UIImage
	init?(url: URL) {
	let filter = CIFilter.qrCodeGenerator()
	filter.message = Data(url.absoluteString.utf8)
	guard let output = filter.outputImage?.transformed(by: CGAffineTransform(scaleX: 8, y: 8)),
	let cgImage = Self.qrContext.createCGImage(output, from: output.extent) else {
	return nil
	}
	image = UIImage(cgImage: cgImage)
	}