[Bug] JwtPayload.Claim.Value should be culture invariant

[huaxing-yuan]

Which version of Microsoft.IdentityModel are you using?
System.IdentityModel.Tokens.Jwt 7.0.3

Where is the issue?

• M.IM.JsonWebTokens
• M.IM.KeyVaultExtensions
• M.IM.Logging
• M.IM.ManagedKeyVaultSecurityKey
• M.IM.Protocols
• M.IM.Protocols.OpenIdConnect
• M.IM.Protocols.SignedHttpRequest
• M.IM.Protocols.WsFederation
• M.IM.TestExtensions
• M.IM.Tokens
• M.IM.Tokens.Saml
• M.IM.Validators
• M.IM.Xml
• S.IM.Tokens.Jwt
• Other (please describe)

Is this a new or an existing app?
c. This is a new app or an experiment.

Repro
Step 1: Set computer localization to one of west european countries, for example "fr-FR", where decimal separator is comma ,.
In these countries, decimal value 10.9 is written as 10,9.
Step 2: Create a JWT with a decimal type claim in the Payload:
Step 3: Get the claim in the payload. The claim.value has a string value 10,9

var credentials = new SigningCredentials(securityKey, algorithm); //whatever signing credentials
var jwtHeader = new JwtHeader(credentials); //whatever headers
var payload = new JwtPayload();
payload.add("numericClaim", 10.9d); //<- here
var token = new JwtSecurityToken(jwtHeader, payload)

Expected behavior
At API level, we would like decimal and datetime data to be represented in invariant culture.
DateTime is perfectly handled with invariant culture: line 522
But all decimal values are not: line 532

azure-activedirectory-identitymodel-extensions-for-dotnet/src/System.IdentityModel.Tokens.Jwt/JwtPayload.cs

Lines 522 to 532 in 5c65369

	claims.Add(new Claim(keyValuePair.Key, dateTime.ToString("o", CultureInfo.InvariantCulture), ClaimValueTypes.DateTime, issuer, issuer));
	else if (keyValuePair.Value is bool boolValue)
	{
	// Can't just use ToString or bools will get encoded as True/False instead of true/false.
	if (boolValue)
	claims.Add(new Claim(keyValuePair.Key, "true", ClaimValueTypes.Boolean, issuer, issuer));
	else
	claims.Add(new Claim(keyValuePair.Key, "false", ClaimValueTypes.Boolean, issuer, issuer));
	}
	else if (keyValuePair.Value != null)
	claims.Add(new Claim(keyValuePair.Key, keyValuePair.Value.ToString(), GetClaimValueType(keyValuePair.Value), issuer, issuer));

Actual behavior
Claim.value is string, from what i have obseved, when the claim is added in the payload with a simple ToString(). The claim value is stored with current culture of the computer (for example: fr-FR, which is not exterchangable with another computer en-US)
https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-

Claim.Value stores "10,9", which is not expected at API/data exchange level. We would like all numeric values to be stored as standard iso format.

Possible solution
I think the behaviour can be fixed in these two lines, by adding a check on numberic types (decimal, double, float, ...) and use invariant culture version of string conversion:

azure-activedirectory-identitymodel-extensions-for-dotnet/src/System.IdentityModel.Tokens.Jwt/JwtPayload.cs

Line 532 in 5c65369

claims.Add(new Claim(keyValuePair.Key, keyValuePair.Value.ToString(), GetClaimValueType(keyValuePair.Value), issuer, issuer));

azure-activedirectory-identitymodel-extensions-for-dotnet/src/System.IdentityModel.Tokens.Jwt/JwtPayload.cs

Line 559 in 5c65369

claims.Add(new Claim(key, obj.ToString(), GetClaimValueType(obj), issuer, issuer));

Additional context / logs / screenshots / links to code
please find here a screenshot of debug info of a generated token: