diff --git a/DOC/READNE.ssl-connection-error b/DOC/READNE.ssl-connection-error
new file mode 100644
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+++ b/DOC/READNE.ssl-connection-error
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+# ----------
+# see also:
+#    https://github.com/lazyfrosch/docker-icingaweb2/issues/1
+#    https://stackoverflow.com/questions/31842400/ssl-issue-after-pear-channel-update-pear-php-net/46544219#46544219
+#
+# possible errors
+#
+#    - download of pgp source code failed
+#      in tha case try to add certificate to ca-certificates file
+#
+#    - pecl runs into error "Connection to `ssl://pecl.php.net:443' failed:"
+#    - pear runs into error "Connection to `ssl://pear.php.net:443' failed:"
+#      in that cases try to add certificate to 'default_cert_file' ..
+#
+# ----------
+
+cert_URL="https://curl.haxx.se/ca/cacert.pem"
+cert_name="$(basename "https://curl.haxx.se/ca/cacert.pem")"
+cert_name_crt="${cert_name%.*}.crt"
+
+
+# ===
+# Add certificate to default certification file (default_cert_file)
+# --
+
+# RUN php -r "print_r(openssl_get_cert_locations());"
+#
+# This will output dfefault ssl certificate locations
+#
+#    Array
+#    (
+#        [default_cert_file] => /usr/lib/ssl/cert.pem
+#        [default_cert_file_env] => SSL_CERT_FILE
+#        [default_cert_dir] => /usr/lib/ssl/certs
+#        [default_cert_dir_env] => SSL_CERT_DIR
+#        [default_private_dir] => /usr/lib/ssl/private
+#        [default_default_cert_area] => /usr/lib/ssl
+#        [ini_cafile] =>
+#        [ini_capath] =>
+#    )
+PHP=/usr/local/php-8.1/bin/php
+_default_cert_file="$($PHP -r "print_r(openssl_get_cert_locations());" | grep -E "\[default_cert_file\]" | awk '{print$3}')"
+
+wget --no-check-certificate -O ${_default_cert_file} "${cert_URL}"
+
+
+# ===
+# add certificate to ca-certificates file
+# ===
+
+_path_to_openssl_dir="$(openssl version -d | awk '{print$2}')"
+_path_to_openssl_dir=${_path_to_openssl_dir#\"}
+_path_to_openssl_dir=${_path_to_openssl_dir%\"}
+_path_to_openssl_dir="$(realpath "${_path_to_openssl_dir}")"
+
+_default_cert_dir="$(realpath "${_path_to_openssl_dir}/certs")"
+
+if [[ -d "/usr/local/share/ca-certificates/" ]] ; then
+   wget --no-check-certificate -O "/usr/local/share/ca-certificates/${cert_name_crt}" "${cert_URL}"
+fi
+
+update-ca-certificates
+c_rehash "${_default_cert_dir}"
+
+
+
+# =====
+# Find the path to the trusted certificates and add certificate there
+# =====
+
+# ---
+# using PHP
+# ---
+#
+# RUN php -r "print_r(openssl_get_cert_locations());"
+#
+# This will output dfefault ssl certificate locations
+#
+#    Array
+#    (
+#        [default_cert_file] => /usr/lib/ssl/cert.pem
+#        [default_cert_file_env] => SSL_CERT_FILE
+#        [default_cert_dir] => /usr/lib/ssl/certs
+#        [default_cert_dir_env] => SSL_CERT_DIR
+#        [default_private_dir] => /usr/lib/ssl/private
+#        [default_default_cert_area] => /usr/lib/ssl
+#        [ini_cafile] =>
+#        [ini_capath] =>
+#    )
+#
+PHP=/usr/local/php-8.1/bin/php
+$PHP -r "print_r(openssl_get_cert_locations());"
+#
+_default_cert_dir="$($PHP -r "print_r(openssl_get_cert_locations());" | grep -E "\[default_cert_dir\]" | awk '{print$3}')"
+_default_cert_dir="$(realpath "${_default_cert_dir}")"
+
+# ---
+# using openssl directly
+# ---
+_path_to_openssl_dir="$(openssl version -d | awk '{print$2}')"
+_path_to_openssl_dir=${_path_to_openssl_dir#\"}
+_path_to_openssl_dir=${_path_to_openssl_dir%\"}
+_path_to_openssl_dir="$(realpath "${_path_to_openssl_dir}")"
+
+
+if [[ ! -d "${_path_to_openssl_dir}/certs" ]] ; then
+   mkdir "${_path_to_openssl_dir}/certs"
+fi
+_default_cert_dir="$(realpath "${_path_to_openssl_dir}/certs")"
+
+
+# ---
+# Download certificate and save it into directory '${_default_cert_dir}'
+# ---
+
+
+wget --no-check-certificate -P "${_default_cert_dir}" "${cert_URL}"
+
+chmod 644 "${_default_cert_dir}/${cert_name}"
+c_rehash "${_default_cert_dir}"
+