SSL certificate verify GitHub action (#13697)

* Implement SSL/TLS certificate checking #782

* SSL: Add nimDisableCertificateValidation

Remove NIM_SSL_CERT_VALIDATION env var
tests/untestable/thttpclient_ssl.nim ran successfully on Linux with libssl 1.1.1d

* SSL: update integ test to skip flapping tests

* Revert .travis.yml change

* nimDisableCertificateValidation disable imports

Prevent loading symbols that are not defined on older SSL libs

* SSL: disable verification in net.nim

..when nimDisableCertificateValidation is set

* Update changelog

* Fix peername type

* Add define check for windows

* Disable test on windows

* Add exprimental GitHub action CI for SSL

* Test nimDisableCertificateValidation

.github/workflows/ci_ssl.yml

@@ -0,0 +1,91 @@
+name: Nim SSL CI
+on:
+  pull_request:
+    # Run only on changes on related files
+    paths:
+      - 'lib/pure/httpclient.nim'
+      - 'lib/pure/net.nim'
+      - 'lib/pure/ssl_certs.nim'
+      - 'lib/wrappers/openssl.nim'
+      - 'tests/stdlib/thttpclient_ssl*'
+      - 'tests/untestable/thttpclient_ssl*'
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-18.04, macos-10.15, windows-2019]
+        cpu: [amd64]
+    name: '${{ matrix.os }} (${{ matrix.cpu }})'
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: 'Checkout'
+        uses: actions/checkout@v2
+
+      - name: 'Checkout csources'
+        uses: actions/checkout@v2
+        with:
+          repository: nim-lang/csources
+          path: csources
+
+      - name: 'Install dependencies (Linux amd64)'
+        if: runner.os == 'Linux' && matrix.cpu == 'amd64'
+        run: |
+          sudo apt-fast update -qq
+          DEBIAN_FRONTEND='noninteractive' \
+            sudo apt-fast install --no-install-recommends -y libssl1.1
+      - name: 'Install dependencies (macOS)'
+        if: runner.os == 'macOS'
+        run: brew install make
+      - name: 'Install dependencies (Windows)'
+        if: runner.os == 'Windows'
+        shell: bash
+        run: |
+          mkdir dist
+          curl -L https://nim-lang.org/download/mingw64.7z -o dist/mingw64.7z
+          curl -L https://nim-lang.org/download/dlls.zip -o dist/dlls.zip
+          7z x dist/mingw64.7z -odist
+          7z x dist/dlls.zip -obin
+          echo "::add-path::${{ github.workspace }}/dist/mingw64/bin"
+
+      - name: 'Add build binaries to PATH'
+        shell: bash
+        run: echo "::add-path::${{ github.workspace }}/bin"
+
+      - name: 'Build 1-stage compiler from csources'
+        shell: bash
+        run: |
+          ncpu=
+          case '${{ runner.os }}' in
+          'Linux')
+            ncpu=$(nproc)
+            ;;
+          'macOS')
+            ncpu=$(sysctl -n hw.ncpu)
+            ;;
+          'Windows')
+            ncpu=$NUMBER_OF_PROCESSORS
+            ;;
+          esac
+          [[ -z "$ncpu" || $ncpu -le 0 ]] && ncpu=1
+
+          make -C csources -j $ncpu CC=gcc ucpu='${{ matrix.cpu }}'
+
+      - name: 'Build koch'
+        shell: bash
+        run: nim c koch
+
+      - name: 'Build the real compiler'
+        shell: bash
+        run: ./koch boot
+
+      - name: 'Run SSL nimDisableCertificateValidation integration tests'
+        shell: bash
+        run: nim c -d:nimDisableCertificateValidation -d:ssl -r -p:. tests/untestable/thttpclient_ssl_disabled.nim
+
+      - name: 'Run SSL certificate check integration tests'
+        # Not supported on Windows due to old openssl version
+        if: runner.os != 'Windows'
+        shell: bash
+        run: nim c -d:ssl -p:. --threads:on -r tests/untestable/thttpclient_ssl.nim