std.http.Client: unable to establish tls connection to GNU Savannah's git repository server

[Techatrix]

Zig Version

0.14.0-dev.2851+b074fb7dd

Steps to Reproduce and Observed Behavior

// sample.zig
const std = @import("std");

pub fn main() !void {
    var arena_allocator = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    const arena = arena_allocator.allocator();

    var client: std.http.Client = .{ .allocator = arena };
    defer client.deinit();
    try client.initDefaultProxies(arena_allocator.allocator());

    const uri = try std.Uri.parse("https://git.savannah.gnu.org/git/readline.git");

    var server_header_buffer: [16 * 1024]u8 = undefined;
    var request = try client.open(.GET, uri, .{
        .server_header_buffer = &server_header_buffer,
    });
    defer request.deinit();
}

$ zig run sample.zig
error: TlsInitializationFailed
/nix/store/8g03rpdq6j91ffa9ww2qchpwd1acn3g2-zig-0.14.0-dev.2851+b074fb7dd/lib/std/crypto/tls.zig:225:32: 0x123cb01 in toError (sample)
            .internal_error => return error.TlsAlertInternalError,
                               ^
/nix/store/8g03rpdq6j91ffa9ww2qchpwd1acn3g2-zig-0.14.0-dev.2851+b074fb7dd/lib/std/crypto/tls/Client.zig:420:17: 0x11f2bcd in init__anon_12350 (sample)
                try desc.toError();
                ^
/nix/store/8g03rpdq6j91ffa9ww2qchpwd1acn3g2-zig-0.14.0-dev.2851+b074fb7dd/lib/std/http/Client.zig:1378:18: 0x1131a8b in connectTcp (sample)
        }) catch return error.TlsInitializationFailed;
                 ^
/nix/store/8g03rpdq6j91ffa9ww2qchpwd1acn3g2-zig-0.14.0-dev.2851+b074fb7dd/lib/std/http/Client.zig:1513:14: 0x11122bf in connect (sample)
    } orelse return client.connectTcp(host, port, protocol);
             ^
/nix/store/8g03rpdq6j91ffa9ww2qchpwd1acn3g2-zig-0.14.0-dev.2851+b074fb7dd/lib/std/http/Client.zig:1661:9: 0x1109277 in open (sample)
        try client.connect(valid_uri.host.?.raw, uriPort(valid_uri, protocol), protocol);
        ^
/home/techatrix/repos/readline/sample.zig:14:19: 0x11086ea in main (sample)
    var request = try client.open(.GET, uri, .{
                  ^

Same result when using zig fetch:

zig fetch git+https://git.savannah.gnu.org/git/readline.git

Expected Behavior

successfully setup a connection

[mocompute]

Related, TLSv1.2 support: #21872

[ianic]

This is the same problem as in issue #21952.

Server chooses cipher suite: TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (0xc030), named group: secp384r1 but Client.zig always uses secp256r1 named group. That line should be sending public key for the named group negotiated with server not a fixed named group.
In this case line should be:

array(u24, u8, array(u8, u8, key_share.secp384r1_kp.public_key.toUncompressedSec1())));

[jedisct1]

Should be fixed by #25007