Use PemEncoding in .NET 5 and later.

This prepares the way to use the new methods that will be added in .NET 10.

Author: bgrainger

src/MySqlConnector/Utilities/Utility.cs

@@ -97,6 +97,11 @@ public static void LoadRsaParameters(string key, RSA rsa)
 	public static RSAParameters GetRsaParameters(string key)
 #endif
 	{
+#if NET5_0_OR_GREATER
+		if (!PemEncoding.TryFind(key, out var pemFields))
+			throw new FormatException(string.Concat("Unrecognized PEM data: ", key.AsSpan(0, Math.Min(key.Length, 80))));
+		var isPrivate = key.AsSpan()[pemFields.Label].SequenceEqual("RSA PRIVATE KEY");
+#else
 		const string beginRsaPrivateKey = "-----BEGIN RSA PRIVATE KEY-----";
 		const string endRsaPrivateKey = "-----END RSA PRIVATE KEY-----";
 		const string beginPublicKey = "-----BEGIN PUBLIC KEY-----";
@@ -135,9 +140,14 @@ public static RSAParameters GetRsaParameters(string key)
 #else
 			throw new FormatException($"Missing expected '{pemFooter}' PEM footer: " + key[Math.Max(key.Length - 80, 0)..]);
 #endif
+#endif
 
 #if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
+#if NET5_0_OR_GREATER
+		var keyChars = key.AsSpan()[pemFields.Base64Data];
+#else
 		var keyChars = key.AsSpan()[keyStartIndex..keyEndIndex];
+#endif
 		var bufferLength = keyChars.Length / 4 * 3;
 		byte[]? buffer = null;
 		Span<byte> bufferBytes = bufferLength > 1024 ?

tests/MySqlConnector.Tests/UtilityTests.cs

@@ -87,9 +87,9 @@ public void ParseTimeSpanFails(string input)
 
 	[Theory]
 	[InlineData("", "")]
-	[InlineData("pre", "")]
-	[InlineData("", "post")]
-	[InlineData("pre", "post")]
+	[InlineData("pre\n", "")]
+	[InlineData("", "\npost")]
+	[InlineData("pre\n", "\npost")]
 	public void DecodePublicKey(string pre, string post)
 	{
 #if NET5_0_OR_GREATER
@@ -105,9 +105,9 @@ public void DecodePublicKey(string pre, string post)
 
 	[Theory]
 	[InlineData("", "")]
-	[InlineData("pre", "")]
-	[InlineData("", "post")]
-	[InlineData("pre", "post")]
+	[InlineData("pre\n", "")]
+	[InlineData("", "\npost")]
+	[InlineData("pre\n", "\npost")]
 	public void DecodePrivateKey(string pre, string post)
 	{
 #if NET5_0_OR_GREATER