Clarify the spec to allow optional or unspecified OAuth scopes (#1888)

* Referencing issue #513. Clarify the spec to accommodate OAuth schemes where scope may be unspecified (optional scope) or where scope is not used at all.

* Removed the provision for default scope represented as empty string. This introduces some ambiguities in the Security Requirement Object that would need to be addressed.

* For #513, adjusting language and removing examples

For #513, adjusting language and removing examples as suggested by @webron.

* removed unnecessary example header

Co-authored-by: Ron <[email protected]>

Author: tedepstein

versions/3.0.3.md

@@ -3294,7 +3294,7 @@ Field Name | Type | Applies To | Description
 <a name="oauthFlowAuthorizationUrl"></a>authorizationUrl | `string` | `oauth2` (`"implicit"`, `"authorizationCode"`) | **REQUIRED**. The authorization URL to be used for this flow. This MUST be in the form of a URL.
 <a name="oauthFlowTokenUrl"></a>tokenUrl | `string` | `oauth2` (`"password"`, `"clientCredentials"`, `"authorizationCode"`) | **REQUIRED**. The token URL to be used for this flow. This MUST be in the form of a URL.
 <a name="oauthFlowRefreshUrl"></a>refreshUrl | `string` | `oauth2` | The URL to be used for obtaining refresh tokens. This MUST be in the form of a URL.
-<a name="oauthFlowScopes"></a>scopes | Map[`string`, `string`] | `oauth2` | **REQUIRED**. The available scopes for the OAuth2 security scheme. A map between the scope name and a short description for it.
+<a name="oauthFlowScopes"></a>scopes | Map[`string`, `string`] | `oauth2` | **REQUIRED**. The available scopes for the OAuth2 security scheme. A map between the scope name and a short description for it. The map MAY be empty.
 
 This object MAY be extended with [Specification Extensions](#specificationExtensions).
 
@@ -3339,7 +3339,6 @@ flows:
       read:pets: read your pets 
 ```
 
-
 #### <a name="securityRequirementObject"></a>Security Requirement Object
 
 Lists the required security schemes to execute this operation.
@@ -3354,7 +3353,7 @@ When a list of Security Requirement Objects is defined on the [OpenAPI Object](#
 
 Field Pattern | Type | Description
 ---|:---:|---
-<a name="securityRequirementsName"></a>{name} | [`string`] | Each name MUST correspond to a security scheme which is declared in the [Security Schemes](#componentsSecuritySchemes) under the [Components Object](#componentsObject). If the security scheme is of type `"oauth2"` or `"openIdConnect"`, then the value is a list of scope names required for the execution. For other security scheme types, the array MUST be empty.
+<a name="securityRequirementsName"></a>{name} | [`string`] | Each name MUST correspond to a security scheme which is declared in the [Security Schemes](#componentsSecuritySchemes) under the [Components Object](#componentsObject). If the security scheme is of type `"oauth2"` or `"openIdConnect"`, then the value is a list of scope names required for the execution, and the list MAY be empty if authorization does not require a specified scope. For other security scheme types, the array MUST be empty.
 
 ##### Security Requirement Object Examples