refactor: tweak SecurityProtocol usage

bin/checkurls.ps1

@@ -38,8 +38,6 @@ Get-ChildItem $Dir "$App.json" | ForEach-Object {
     $Queue += , @($_.Name, $manifest)
 }
 
-$original = use_any_https_protocol
-
 Write-Host '[' -NoNewLine
 Write-Host 'U' -NoNewLine -ForegroundColor Cyan
 Write-Host ']RLs'
@@ -130,5 +128,3 @@ foreach ($man in $Queue) {
         Write-Host "       > $_" -ForegroundColor DarkRed
     }
 }
-
-set_https_protocols $original

bin/checkver.ps1

@@ -89,8 +89,6 @@ Get-Event | ForEach-Object {
     Remove-Event $_.SourceIdentifier
 }
 
-$original = use_any_https_protocol
-
 # start all downloads
 $Queue | ForEach-Object {
     $name, $json = $_
@@ -287,5 +285,3 @@ while ($in_progress -gt 0) {
         }
     }
 }
-
-set_https_protocols $original

lib/core.ps1

@@ -20,12 +20,23 @@ $cachedir = $env:SCOOP_CACHE, "$scoopdir\cache" | Select-Object -first 1
 
 # Note: Github disabled TLS 1.0 support on 2018-02-23. Need to enable TLS 1.2
 # for all communication with api.github.com
-function enable-encryptionscheme([Net.SecurityProtocolType]$scheme) {
-    # Net.SecurityProtocolType is a [Flags] enum, binary-OR sets
-    # the specified scheme in addition to whatever scheme is already active
-    [Net.ServicePointManager]::SecurityProtocol = [Net.ServicePointManager]::SecurityProtocol -bor $scheme
-}
-enable-encryptionscheme "Tls12"
+function Optimize-SecurityProtocol {
+    # .NET Framework 4.7+ has a default security protocol called 'SystemDefault',
+    # which allows the operating system to choose the best protocol to use.
+    # If SecurityProtocolType contains 'SystemDefault' (means .NET4.7+ detected)
+    # and the value of SecurityProtocol is 'SystemDefault', just do nothing on SecurityProtocol,
+    # 'SystemDefault' will use TLS 1.2 if the webrequest requires.
+    $isNewerNetFramework = ([System.Enum]::GetNames([System.Net.SecurityProtocolType]) -contains 'SystemDefault')
+    $isSystemDefault = ([System.Net.ServicePointManager]::SecurityProtocol.Equals([System.Net.SecurityProtocolType]::SystemDefault))
+
+    # If not, change it to support TLS 1.2
+    if (!($isNewerNetFramework -and $isSystemDefault)) {
+        # Set to TLS 1.2 (3072), then TLS 1.1 (768), and TLS 1.0 (192). Ssl3 has been superseded,
+        # https://docs.microsoft.com/en-us/dotnet/api/system.net.securityprotocoltype?view=netframework-4.5
+        [System.Net.ServicePointManager]::SecurityProtocol = 3072 -bor 768 -bor 192
+    }
+}
+Optimize-SecurityProtocol
 
 function Get-UserAgent() {
     return "Scoop/1.0 (+http://scoop.sh/) PowerShell/$($PSVersionTable.PSVersion.Major).$($PSVersionTable.PSVersion.Minor) (Windows NT $([System.Environment]::OSVersion.Version.Major).$([System.Environment]::OSVersion.Version.Minor); $(if($env:PROCESSOR_ARCHITECTURE -eq 'AMD64'){'Win64; x64; '})$(if($env:PROCESSOR_ARCHITEW6432 -eq 'AMD64'){'WOW64; '})$PSEdition)"

lib/install.ps1

@@ -113,26 +113,7 @@ function dl_with_cache($app, $version, $url, $to, $cookies = $null, $use_cache =
     }
 }
 
-function use_any_https_protocol() {
-    $original = "$([System.Net.ServicePointManager]::SecurityProtocol)"
-    $available = [string]::join(', ', [Enum]::GetNames([System.Net.SecurityProtocolType]))
-
-    # use whatever protocols are available that the server supports
-    set_https_protocols $available
-
-    return $original
-}
-
-function set_https_protocols($protocols) {
-    try {
-        [System.Net.ServicePointManager]::SecurityProtocol = [System.Net.SecurityProtocolType] $protocols
-    } catch {
-        [System.Net.ServicePointManager]::SecurityProtocol = "Tls,Tls11,Tls12"
-    }
-}
-
 function do_dl($url, $to, $cookies) {
-    $original_protocols = use_any_https_protocol
     $progress = [console]::isoutputredirected -eq $false -and
         $host.name -ne 'Windows PowerShell ISE Host'
 
@@ -143,8 +124,6 @@ function do_dl($url, $to, $cookies) {
         $e = $_.exception
         if($e.innerexception) { $e = $e.innerexception }
         throw $e
-    } finally {
-        set_https_protocols $original_protocols
     }
 }