google-cloud-cpp 3.10.0 fails to build with OpenSSL 4.x due to X509_get_subject_name() constness

[hiroyuki-sato]

Does this issue affect the google-cloud-cpp project?

Yes. This is a build issue in the google-cloud-cpp client library itself.

What component of google-cloud-cpp is this related to?

This is related to the OpenSSL code in google/cloud/internal/openssl, specifically parse_service_account_p12_file.cc.

Describe the bug A clear and concise description of what the bug is.

google-cloud-cpp 3.10.0 fails to build with OpenSSL 4.x.

It appears that X509_get_subject_name() returns const X509_NAME * with OpenSSL 4.x, while the current code assigns the result to X509_NAME *.

The build fails with the following error:

/tmp/google-cloud-cpp-3.10.0/google/cloud/internal/openssl/parse_service_account_p12_file.cc:88:14: error:
      cannot initialize a variable of type 'X509_NAME *' (aka 'X509_name_st *')
      with an rvalue of type 'const X509_NAME *' (aka 'const X509_name_st *')
   88 |   X509_NAME* name = X509_get_subject_name(cert.get());
      |              ^      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

To Reproduce Steps to reproduce the behavior:

Install OpenSSL 4.x with Homebrew.

brew install openssl@4

Configure google-cloud-cpp 3.10.0 to use OpenSSL 4.x.

cmake -S . -B build \
  -DBUILD_TESTING=OFF \
  -DOPENSSL_ROOT_DIR="$(brew --prefix openssl@4)"

Build google-cloud-cpp.

cmake --build build -j

The build fails while compiling google/cloud/internal/openssl/parse_service_account_p12_file.cc.

Expected behavior A clear and concise description of what you expected to
happen.

google-cloud-cpp should build successfully with OpenSSL 4.x, or the supported OpenSSL versions should exclude OpenSSL 4.x.

Operating system:

macOS 26.7

What compiler and version are you using?

Apple clang version 21.0.0 (clang-2100.3.34.2)

What version of google-cloud-cpp are you using?

google-cloud-cpp 3.10.0

Additional context

This issue was originally discovered in the Apache Arrow CI build.

OpenSSL was installed using Homebrew:

$ /opt/homebrew/opt/openssl@4/bin/openssl version
OpenSSL 4.0.2 25 Aug 2026 (Library: OpenSSL 4.0.2 25 Aug 2026)