Using the PEM format will be required until libssh2 implements support for other formats or Julia replaces libgit2/libssh2 with command line git for Pkg operations. This is nothing new, what has changed is that OpenSSH switched default output format for ssh-keygen in version 7.8. See SSH auth keys, just very painful outside of ssh-agent. · Issue #911 · JuliaLang/Pkg.jl · GitHub for some more details.
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