Add patch for client credential support to cpprest package.

[abeltrano]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• The toolchain has been rebuilt successfully (or no changes were made to it)
• The toolchain/worker package manifests are up-to-date
• Any updated packages successfully build (or no packages were changed)
• All package sources are available
• cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/tools/cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json)
• LICENSE-MAP files are up-to-date (./SPECS/LICENSES-AND-NOTICES/LICENSES-MAP.md, ./SPECS/LICENSES-AND-NOTICES/LICENSE-EXCEPTIONS.PHOTON)
• All source files have up-to-date hashes in the *.signatures.json files
• sudo make go-tidy-all and sudo make go-test-coverage pass
• Documentation has been updated to match any changes to the build system
• Ready to merge

• NOTE: I could not get the build-packages make target to work, so instead, rebuilt this package using rpmbuild directly.

---

Summary

Add support for OAuth2 client credentials grant type to the cpprest package. This grant type is commonly used in the absence of a user, so is useful for applications involving IoT devices.

Change Log

• Add cpprest-2.10.14-Add-support-for-oauth2-using-client-credentials.patch, enabling grant type 'client_credentials'.

Does this affect the toolchain?

NO

Associated issues

• Support for oauth2 with "client_credentials" grant type  cpprestsdk#1496

Test Methodology

• Local package build of cpprestsdk package.
• This patch has been used successfully since 09/15/2020 in a Mariner-derivative at Microsoft for an Azure project, using the same base version of cppresksdk (2.10.14). The package is used by two other packages in the derivative.

[abeltrano]

spec-lint checks required this change, and the others where existing lines in this file were moved.

[jslobodzian]

Is this a public API change?

[abeltrano]

This particular change to http_constants.dat is part of a private header (include/cpprest/details), so no. This adds a const std::string to a private helper class, as below (note the details namespace):

/// oAuth 2.0 library.
namespace oauth2
{
namespace details
{
class oauth2_handler;

// Constant strings for OAuth 2.0.
typedef utility::string_t oauth2_string;
class oauth2_strings
{
public:
#define _OAUTH2_STRINGS
#define DAT(a_, b_) _ASYNCRTIMP static const oauth2_string a_;
#include "cpprest/details/http_constants.dat"
#undef _OAUTH2_STRINGS
#undef DAT
};

} // namespace details

To add some more color, the added constant client_credentials is used in the impl of a newly added public function token_from_client_credentials() to add a uri parameter requiring a specific name for the oauth2 protocol. Since this is a new function that must be called explicitly, there should be no way for it to cause back-compat issues.

[abeltrano]

After discussion with @jslobodzian, we'll rescind this PR until the change is accepted in the upstream cpprest repo.