function ca_chain!(context::SSLContext, crt_file, key_file)
    res = ccall((:SSL_CTX_use_certificate_file, libssl), Cint, (Ptr{Cvoid}, Cstring, Cint),
                context.ptr, crt_file, SSL_FILETYPE_PEM)
    if res <= 0
        @error res
    end
    res = ccall((:SSL_CTX_use_PrivateKey_file, libssl), Cint, (Ptr{Cvoid}, Cstring, Cint),
                context.ptr, key_file, SSL_FILETYPE_PEM)
    if res <= 0
        @error res
    end
    if ccall((:SSL_CTX_check_private_key, libssl), Cint, (Ptr{Cvoid}, ), context.ptr) != 1
        @error "Private and certificate is not matching"
    end
    return nothing
end

get_peer_certificate(client::SSLClient) =
    ccall((:SSL_get_peer_certificate, libssl), Ptr{Cvoid}, (Ptr{Cvoid},), client.ssl)

verify_certificate(client::SSLClient) =
    ccall((:SSL_get_verify_result, libssl), Clong, (Ptr{Cvoid},),
          client.ssl)

function X509_get_serialNumber(X509)
    asn_ptr = ccall((:X509_get_serialNumber, libssl), Ptr{Cvoid}, (Ptr{Cvoid},), X509)
    res = Ref{Clong}(0)
    # TODO: check return value (1:ok)
    # TODO: Move to own func and call it
    n = ccall((:ASN1_INTEGER_get_int64, libssl), Cint, (Ref{Clong},Ptr{Cvoid}),
              res, asn_ptr)
    res[]
end

function X509_digest(X509; md_type = EVP_sha1())
    len = Ref{Cint}(0)
    md = zeros(UInt8, EVP_MAX_MD_SIZE)
    res = ccall((:X509_digest, libssl), Cint,
                (Ptr{Cvoid}, Ptr{Cvoid}, Ref{Cuchar}, Ref{Cint}),
                X509, md_type, md, len) == 1
    !res && throw("Error")
    md[1:len[]]
end

digest_to_string(d::Array{UInt8}) = join(string.(d, base = 16), ":")
digest_to_string_62(d::Vector{T}) where T  = join(string.(reinterpret(UInt32, d), base = 62), ":")