Improvements to key loading helpers

[prince-chrismc]

We should deprecate/remove the older helpers and rename them to have RSA in the name.

Originally posted by @prince-chrismc in #185 (comment)

[prince-chrismc]

I also switched from [pem_bio_read]. This change made it obvious that one could use the same code for reading RSA and EC keys. The functions only differ in type of errors they report, e.g., error::ecdsa_error::create_mem_bio_failed vs. error::rsa_error::create_mem_bio_failed.

Orignally posted in #185 (comment)

[prince-chrismc]

The newer EC family of helpers are also missing test code which was present with the old ones load_public_ec_key_from_string for example

[prince-chrismc]

The implementations are nearly the same they just need different error codes but otherwise are interchangable

diff --git a/include/jwt-cpp/jwt.h b/include/jwt-cpp/jwt.h
index 000fb0b..1235585 100644
--- a/include/jwt-cpp/jwt.h
+++ b/include/jwt-cpp/jwt.h
@@ -778,7 +778,7 @@ namespace jwt {
                        ec.clear();
                        auto pubkey_bio = make_mem_buf_bio();
                        if (!pubkey_bio) {
-                               ec = error::ecdsa_error::create_mem_bio_failed;
+                               ec = error::rsa_error::create_mem_bio_failed;
                                return {};
                        }
                        if (key.substr(0, 27) == "-----BEGIN CERTIFICATE-----") {
@@ -786,13 +786,13 @@ namespace jwt {
                                if (ec) return {};
                                const int len = static_cast<int>(epkey.size());
                                if (BIO_write(pubkey_bio.get(), epkey.data(), len) != len) {
-                                       ec = error::ecdsa_error::load_key_bio_write;
+                                       ec = error::rsa_error::load_key_bio_write;
                                        return {};
                                }
                        } else {
                                const int len = static_cast<int>(key.size());
                                if (BIO_write(pubkey_bio.get(), key.data(), len) != len) {
-                                       ec = error::ecdsa_error::load_key_bio_write;
+                                       ec = error::rsa_error::load_key_bio_write;
                                        return {};
                                }
                        }
@@ -800,7 +800,7 @@ namespace jwt {
                        evp_pkey_handle pkey(PEM_read_bio_PUBKEY(
                                pubkey_bio.get(), nullptr, nullptr,
                                (void*)password.data())); // NOLINT(google-readability-casting) requires `const_cast`
-                       if (!pkey) ec = error::ecdsa_error::load_key_bio_read;
+                       if (!pkey) ec = error::rsa_error::load_key_bio_read;
                        return pkey;
                }

[ RUN      ] OpenSSLErrorTest.LoadECDSAPrivateKeyFromString
/home/runner/work/jwt-cpp/jwt-cpp/tests/OpenSSLErrorTest.cpp:478: Failure
Expected equality of these values:
  ec
    Which is: rsa_error:17
  e.expected_ec
    Which is: ecdsa_error:12
[  FAILED  ] OpenSSLErrorTest.LoadECDSAPrivateKeyFromString (0 ms)
[ RUN      ] OpenSSLErrorTest.LoadECDSAPublicKeyFromString
/home/runner/work/jwt-cpp/jwt-cpp/tests/OpenSSLErrorTest.cpp:478: Failure
Expected equality of these values:
  ec
    Which is: rsa_error:17
  e.expected_ec
    Which is: ecdsa_error:12
[  FAILED  ] OpenSSLErrorTest.LoadECDSAPublicKeyFromString (0 ms)
[ RUN      ] OpenSSLErrorTest.ECDSACertificate
/home/runner/work/jwt-cpp/jwt-cpp/tests/OpenSSLErrorTest.cpp:478: Failure
Expected equality of these values:
  ec
    Which is: rsa_error:17
  e.expected_ec
    Which is: ecdsa_error:12

[prince-chrismc]

Should be possible with some more templates compiler explorer