https://github.com/uhoreg/matrix-doc/blob/cross-signing2/proposals/1756-cross-signing.md https://github.com/uhoreg/matrix-doc/blob/cross-signing2/pro... is the

https://github.com/uhoreg/matrix-doc/blob/cross-signing2/proposals/1756-cross-signing.md https://github.com/uhoreg/matrix-doc/blob/cross-signing2/pro... is the spec for this, fwiw