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Using TLS 1.2 on .net 6

Is there any way to force my .net 6.0 application to use TLS 1.2? Im sadly forced to use TLS 1.2 by an API that is yet to be updated and i would prefer to not make a lot of loopholes to run 4.7/4.8 just to get TLS 1.2.

Forcing .NET application to use TLS 1.2 or later

I wonder how to force a .NET application targeting .NET Framework 4.8 to use TLS 1.2 or later (including future TLS versions).
The application execute as a Windows service. For >98% of the users, it is correctly using TLS 1.2 but in a couple of cases it tries to use older versions like TLS 1.0 or even SSL 3.0. The users who have had issues with it using older TLS versions has been able to resolve it by making registry changes, but telling users to reconfigure settings in Windows registry is a bit risky.
I have followed Microsofts recommendation to not hardcoded the application to use a specific TLS version and instead just rely on the OS default (https://learn.microsoft.com/en-us/dotnet/framework/network-programming/tls).
So what I wonder is: Is there some way in a .NET application to:
Use the Windows default TLS version if it's TLS 1.2 or later.
If the Windows default TLS version is SSL 3.0, TLS 1.0 or TLS 1.1 then use TLS 1.2 or later (including TLS 1.3)
I know I can hardcode the TLS version using ServicePointManager.SecurityProtocol, but this goes against Microsofts recommendation and if I hardcode it to TLS 1.2 and 1.3, then whenever TLS 1.4 is used and the customers OS is patched to support it, my application will still use TLS 1.3 which I don't want.

What about adding TLS declaration before calling the action
public static void UploadFile()
{
System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12;
}

How to fix to use TLS 1.2

I am using Windows 10, Visual Studio 2017, .Net 4.7.
And using DocuSign SOAP APIs to send an envelope. My code is using .NET 4.7 - checked in web.config and confirmed in project properties > Application tab.
And yet, I keep getting the error from DocuSign that I need to use TLS 1.2 and that I am using TLS 1.
What else can I do to fix this?

You can always force the TLS version yourself with:
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
However, this shouldn't be necessary under .NET Framework 4.7. TLS 1.2 is the default.
See also this blog post from Docusign.

.NET Framework 3.5 and TLS 1.2

I currently have a web application that uses the .NET 3.5 framework and I am wondering if it will be compatible with TLS 1.2. No where in our code are we dictating TLS version. This is a legacy application and recompiling is not on the table right now. I am not finding much info on whether you can or cannot, but I was under the impression that compatibility is more dependent on the OS version. It looks like the minimum is 2008 R2. The goal is to get paypal to communicate properly come July 1st.

As was mentioned .net 3.5.1 DOES now support TLS 1.2; but you don't need the registry changes mentioned by #Paulina's answer.
I'm using VS 2008 with .net 3.5.30729.4926. All I had to do was:
Add imports:
Imports System.Security.Authentication
Imports System.Net
Add this to my code (C#):
public const SslProtocols _Tls12 = (SslProtocols)0x00000C00;
public const SecurityProtocolType Tls12 = (SecurityProtocolType)_Tls12;
ServicePointManager.SecurityProtocol = Tls12
VB.net version:
Const _Tls12 As SslProtocols = DirectCast(&HC00, SslProtocols)
Const Tls12 As SecurityProtocolType = DirectCast(_Tls12, SecurityProtocolType)
ServicePointManager.SecurityProtocol = Tls12
Culled from: https://support.microsoft.com/en-us/help/3154518/support-for-tls-system-default-versions-included-in-the-.net-framework Note: by defining the const in my code I could ignore everything else in the article including the registry edits and cs files.

As you can see from the docs, TLS 1.2 is not in the enumeration for SslProtocols, it was added to the enum in .NET 4.5 (thanks #orhun).
There is no workaround for TLS 1.2 compatibility on .NET 3.5.
Unfortunately you will have to upgrade to .NET 4.5 or later to get TLS 1.2 compatibility.
EDIT 10/11/17
My above answer is no longer accurate. In May of 2017, Microsoft released a package to allow TLS 1.2 in .NET 3.5.1.

You can make TLS 1.2 work with Framework 3.5.
Microsoft have released update for it.
Follow this steps
Install Support update for TLS in Framework 3.5 from here:
https://support.microsoft.com/en-us/help/3154518/support-for-tls-system-default-versions-included-in-the-.net-framework-3.5.1-on-windows-7-sp1-and-server-2008-r2-sp1
Go to registry
Type regedit in start
Right click and run as administrator
Navigate to registry keys
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v2.0.50727]
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v2.0.50727]
Right click on the registry key and click Export
Name the file and save it with .reg extension (keep them as your backup in case you need to restore them)
Add entry to registry keys
Make copy of the saved files and rename them
Open with text editor and add following text to each key (this is for 64-bit operating system) and save changes (for 32-bit operating system look at the info in the link)
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v2.0.50727]
"SystemDefaultTlsVersions"=dword:00000001
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v2.0.50727]
"SystemDefaultTlsVersions"=dword:00000001
Double click on the file and click Yes on the window to allow changes
Add code to your project as specified in the link - Developer Guidance section
I applied this solution and it worked for me.

I have just verified that this is all you need in your code to enable support for TLS 1.2 in .NET Framework 3.5:
ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;
I verified by creating a unit test in .NET Framework 3.5 that fetches this HTML page: https://clienttest.ssllabs.com:8443/ssltest/viewMyClient.html
Without the above line, the TLS test page says that I'm using TLS 1.0, which is .NET 3.5's default.
TLS 1.1 is deprecated along with 1.0, but if you want to enable it as well, you can use this line instead (not recommended):
ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072 | (SecurityProtocolType)768;
The "magic" values 3072 and 768 are taken from .NET Framework 4.5's version of the SecurityProtocolType enum:
192: Specifies the TLS 1.0 security protocol
768: Specifies the TLS 1.1 security protocol
3072: Specifies the TLS 1.2 security protocol
I'm not sure whether the server running this code has to have .NET Framework 4.5 runtime installed or not, but it could be so.

I am having the same problem as the OP - old .net 3.5 code having to connect to an external service using tls 1.2.
As mentioned in the accepted answer there is a patch for tls1.2 released by MS.
After this they have released a patch for Server 2008 (not R2):
https://cloudblogs.microsoft.com/microsoftsecure/2017/07/20/tls-1-2-support-added-to-windows-server-2008/
So it should be possible to upgrade to tls 1.2 while still running server 2008.

Does TLS 1.2 support depend only on the version of the .NET framework?

I want to globally enforce using TLS 1.2 in my WPF application in the following way:
System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12;
From .NET 4.5 TLS 1.2 protocol is supported for secure communication over https. My question is that will this always work if I ship the .NET 4.5 along side with my application. Does it depends on the OS version?

TLS is termintated in Windows by a component called SChannel. The supported ciphers are dependent on the version of SChannel, which is dependent on the OS, NOT on the .Net version. Windows XP for instance, only supports up to TLS 1.0
This means that your host PC needs to be at least Windows 7 if you want to support TLS 1.2
Details can be found here: http://blogs.msdn.com/b/kaushal/archive/2011/10/02/support-for-ssl-tls-protocols-on-windows.aspx