`SecurityContextHolderThreadLocalAccessor` currently propagates the
same `SecurityContext` to other threads when Micrometer
Context Propagation is used. This leads to unintended sharing of
mutable state and can cause authentication to leak between threads.
This change updates the accessor to create a new
`SecurityContext` for the target thread while reusing only the
`Authentication` value. Each thread now receives its own
`SecurityContext` instance, preventing cross-thread interference and
aligning with recommended `SecurityContext` usage.
Signed-off-by: Tadaya Tsuyukubo <tadaya@ttddyy.net>
Tadaya Tsuyukubo
d111029078