Add script to sign the APK.

tools/sign_apk.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+
+set -e
+
+if [[ -z "${ANDROID_HOME}" ]]; then
+    echo "Env variable ANDROID_HOME is not set, should be set to something like ~/Library/Android/sdk"
+    exit 1
+fi
+
+if [[ "$#" -ne 2 ]]; then
+  echo "Usage: $0 KEYSTORE_PATH APK" >&2
+  exit 1
+fi
+
+# Get the command line parameters
+PARAM_KEYSTORE_PATH=$1
+PARAM_APK=$2
+
+# Other params
+BUILD_TOOLS_VERSION="28.0.3"
+MIN_SDK_VERSION=19
+
+echo "Signing APK with build-tools version ${BUILD_TOOLS_VERSION} for min SDK version ${MIN_SDK_VERSION}..."
+
+APK_SIGNER_PATH=${ANDROID_HOME}/build-tools/${BUILD_TOOLS_VERSION}
+
+${APK_SIGNER_PATH}/apksigner sign \
+    -v \
+    --ks ${PARAM_KEYSTORE_PATH} \
+    --min-sdk-version ${MIN_SDK_VERSION} \
+    ${PARAM_APK}
+
+# Verify the signature
+echo "Verifying the signature..."
+
+# Note: we ignore warning on META-INF files
+${APK_SIGNER_PATH}/apksigner verify \
+    -v \
+    --min-sdk-version ${MIN_SDK_VERSION} \
+    ${PARAM_APK} \
+    | grep -v "WARNING: META-INF/"
+
+echo
+echo "Congratulations! The APK ${PARAM_APK} is now signed!"