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Showing content from https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1068 below:

CA1068: CancellationToken parameters must come last (code analysis) - .NET

A method has a CancellationToken parameter that is not the last parameter.

By default, this rule analyzes the entire codebase, but this is configurable.

Methods that perform long running operations or asynchronous operations and are cancelable normally take a cancellation token parameter. Each cancellation token has a CancellationTokenSource that creates the token and uses it for cancelable computations. It is common practice to have a long chain of method calls that pass around the cancellation token from the callers to the callees. Hence, a large number of methods that take part in a cancelable computation end up having a cancellation token parameter. However, the cancellation token itself is not usually relevant to the core functionality of a majority of these methods. It's considered a good API design practice to have such parameters be the last parameter in the list.

Rule CA1068 does not fire in the following special cases:

• Method has one or more optional parameters (Optional in Visual Basic) following a non-optional cancellation token parameter. The compiler requires that all optional parameters are defined after all the non-optional parameters.
• Method has one or more ref or out parameters (ByRef in Visual Basic) following a cancellation token parameter. It is common practice to have ref or out parameters be at the end of the list, because they usually indicate output values for the method.

Change the method signature to move the cancellation token parameter to the end of the list. For example, the following two code snippets show a violation of the rule and how to fix it:

// Violates CA1068
public void LongRunningOperation(CancellationToken token, string usefulParameter)
{
    ...
}

// Does not violate CA1068
public void LongRunningOperation(string usefulParameter, CancellationToken token)
{
    ...
}

If the method is an externally visible public API that is already part of a shipped library, then it is safe to suppress a warning from this rule to avoid a breaking change for the library consumers.

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA1068
// The code that's violating the rule is on this line.
#pragma warning restore CA1068

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA1068.severity = none

For more information, see How to suppress code analysis warnings.

Use the following options to configure which parts of your codebase to run this rule on.

• Include specific API surfaces
• Exclude specific symbols
• Exclude specific types and their derived types

You can configure these options for just this rule, for all rules they apply to, or for all rules in this category (Design) that they apply to. For more information, see Code quality rule configuration options.

You can configure which parts of your codebase to run this rule on, based on their accessibility, by setting the api_surface option. For example, to specify that the rule should run only against the non-public API surface, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.api_surface = private, internal

Note

Replace the XXXX part of CAXXXX with the ID of the applicable rule.

You can exclude specific symbols, such as types and methods, from analysis by setting the excluded_symbol_names option. For example, to specify that the rule should not run on any code within types named MyType, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.excluded_symbol_names = MyType

Note

Replace the XXXX part of CAXXXX with the ID of the applicable rule.

Allowed symbol name formats in the option value (separated by |):

• Symbol name only (includes all symbols with the name, regardless of the containing type or namespace).
• Fully qualified names in the symbol's documentation ID format. Each symbol name requires a symbol-kind prefix, such as M: for methods, T: for types, and N: for namespaces.
• .ctor for constructors and .cctor for static constructors.

Examples:

You can exclude specific types and their derived types from analysis by setting the excluded_type_names_with_derived_types option. For example, to specify that the rule should not run on any methods within types named MyType and their derived types, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.excluded_type_names_with_derived_types = MyType

Note

Replace the XXXX part of CAXXXX with the ID of the applicable rule.

Allowed symbol name formats in the option value (separated by |):

• Type name only (includes all types with the name, regardless of the containing type or namespace).
• Fully qualified names in the symbol's documentation ID format, with an optional T: prefix.

Examples:

• CA1021: Avoid out parameters

• Recommended patterns for CancellationToken

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