Can't Build Caddy with Module Flagr

[stevancris]

Hola!

Currently, I want to build Caddy with module flagr on my local, but I face an error when building. The error is

2023/09/07 10:28:51 [INFO] exec (timeout=0s): /usr/local/go/bin/go get -d -v github.com/RussellLuo/caddy-ext/flagr github.com/caddyserver/caddy/v2 
panic: internal error: can't find reason for requirement on golang.org/x/[email protected]

goroutine 1 [running]:
cmd/go/internal/modget.(*resolver).updateBuildList.func1({{0xc00097f7d0?, 0xc001108720?}, {0xc00033a360?, 0xc001414a20?}})
        /usr/local/go/src/cmd/go/internal/modget/get.go:1760 +0x114
cmd/go/internal/modget.(*resolver).updateBuildList(0xc000222000, {0xb313d0, 0xc00019a000}, {0x0, 0x0, 0x0})
        /usr/local/go/src/cmd/go/internal/modget/get.go:1765 +0x597
cmd/go/internal/modget.(*resolver).applyUpgrades(0xc000222000, {0xb313d0, 0xc00019a000}, {0x0?, 0x2?, 0x472485?})
        /usr/local/go/src/cmd/go/internal/modget/get.go:1312 +0x105
cmd/go/internal/modget.runGet({0xb313d0, 0xc00019a000}, 0xc0001c4510?, {0xc0001ae160, 0x2, 0x2})
        /usr/local/go/src/cmd/go/internal/modget/get.go:351 +0x45e
main.invoke(0xe2d000, {0xc0001ae130, 0x5, 0x5})
        /usr/local/go/src/cmd/go/main.go:225 +0x34e
main.main()
        /usr/local/go/src/cmd/go/main.go:179 +0x7d1
2023/09/07 10:28:53 [FATAL] exit status 2

Then, I tried to download caddy with module flagr on the web https://caddyserver.com/download?package=github.com%2FRussellLuo%2Fcaddy-ext%2Fflagr, and got the same issue. The error is like the picture below

I try to access the https://golang.org/x/[email protected] is get a response 404 page not found