JWT Authentication and Swagger with .NET Core 3.0

If you are using Swagger 3.0 then it has build-in support for JWT authentication.

You need to use ParameterLocation.Header, SecuritySchemeType.Http, bearer, and JWT in OpenApiSecurityScheme as shown below.

After this, you wouldn't need to specify token in Bearer {token} format. Only specify the token and the security scheme will automatically apply it in the header.

// Bearer token authentication
OpenApiSecurityScheme securityDefinition = new OpenApiSecurityScheme()
{
    Name = "Bearer",
    BearerFormat = "JWT",
    Scheme = "bearer",
    Description = "Specify the authorization token.",
    In = ParameterLocation.Header,
    Type = SecuritySchemeType.Http,
};
c.AddSecurityDefinition("jwt_auth", securityDefinition);

// Make sure swagger UI requires a Bearer token specified
OpenApiSecurityScheme securityScheme = new OpenApiSecurityScheme()
{
    Reference = new OpenApiReference()
    {
        Id = "jwt_auth",
        Type = ReferenceType.SecurityScheme
    }
};
OpenApiSecurityRequirement securityRequirements = new OpenApiSecurityRequirement()
{
    {securityScheme, new string[] { }},
};
c.AddSecurityRequirement(securityRequirements);

After some research, I eventually found the answer here

Before seeing this page, I knew that I should use AddSecurityRequirement after AddSecurityDefinition because of many samples, but it was a problem that the function parameters have changed on .NET Core 3.0.

By the way, the final answer is as below:

services.AddSwaggerGen(c =>
{
  c.SwaggerDoc("v1", new OpenApiInfo { 
    Title = "My API", 
    Version = "v1" 
  });
  c.AddSecurityDefinition("Bearer", new OpenApiSecurityScheme {
    In = ParameterLocation.Header, 
    Description = "Please insert JWT with Bearer into field",
    Name = "Authorization",
    Type = SecuritySchemeType.ApiKey 
  });
  c.AddSecurityRequirement(new OpenApiSecurityRequirement {
   { 
     new OpenApiSecurityScheme 
     { 
       Reference = new OpenApiReference 
       { 
         Type = ReferenceType.SecurityScheme,
         Id = "Bearer" 
       } 
      },
      new string[] { } 
    } 
  });
});