extmod/mbedtls: enable PEM parsing.#145
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The mbedtls config built only DER support, so the ssl module could load certificates and keys only in DER form, and `load_verify_locations` could hold just a single certificate (mbedtls >= 3.5 rejects DER buffers with trailing bytes, so concatenated DER doesn't work either). Enable MBEDTLS_PEM_PARSE_C (with its required MBEDTLS_BASE64_C) so the stack accepts PEM directly -- the format every tool emits -- and so a single `load_verify_locations(cadata=...)` can load multiple concatenated PEM certificates as a CA bundle (mbedtls_x509_crt_parse iterates PEM blocks). This is needed to verify public servers whose issuing CA rotates among several roots, where pinning one root is fragile. Costs a few KB of flash for base64 + PEM. Signed-off-by: Kwabena W. Agyeman <kwagyeman@live.com>
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The mbedtls config built only DER support, so the ssl module could load certificates and keys only in DER form, and
load_verify_locationscould hold just a single certificate (mbedtls >= 3.5 rejects DER buffers with trailing bytes, so concatenated DER doesn't work either).Enable MBEDTLS_PEM_PARSE_C (with its required MBEDTLS_BASE64_C) so the stack accepts PEM directly -- the format every tool emits -- and so a single
load_verify_locations(cadata=...)can load multiple concatenated PEM certificates as a CA bundle (mbedtls_x509_crt_parse iterates PEM blocks). This is needed to verify public servers whose issuing CA rotates among several roots, where pinning one root is fragile. Costs a few KB of flash for base64 + PEM.