你能试试这样吗，

import android.os.Bundle
import android.webkit.WebChromeClient
import android.webkit.WebResourceRequest
import android.webkit.WebView
import android.webkit.WebViewClient
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {
    lateinit var webView: WebView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        webView = findViewById(R.id.webView)
        webView.settings.javaScriptEnabled = true

        val username = "your_username"
        val password = "your_password"

        val loginButton = findViewById(R.id.loginButton)
        loginButton.setOnClickListener {
            // Load the login page
            webView.loadUrl("http://example.com/login")
        }

        webView.webViewClient = object : WebViewClient() {
            override fun onPageFinished(view: WebView?, url: String?) {
                super.onPageFinished(view, url)
                // Inject JavaScript to autofill and submit the login form
                val jsCode = """
                    document.querySelector('input[name="username"]').value = "$username";
                    document.querySelector('input[name="password"]').value = "$password";
                    document.querySelector('button[type="submit"]').click();
                """.trimIndent()
                webView.evaluateJavascript(jsCode, null)
            }
        }
    }
}

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