diff --git a/Sources/Flows/OAuth2.swift b/Sources/Flows/OAuth2.swift
index 896aa67..a655661 100644
--- a/Sources/Flows/OAuth2.swift
+++ b/Sources/Flows/OAuth2.swift
@@ -21,6 +21,7 @@
 import Foundation
 #if !NO_MODULE_IMPORT
  import Base
+ import Constants
  #if os(macOS)
   import macOS
  #elseif os(iOS) || os(visionOS)
@@ -358,7 +359,7 @@ open class OAuth2: OAuth2Base {
 		}
 		
 		let req = OAuth2AuthRequest(url: (clientConfig.refreshURL ?? clientConfig.tokenURL ?? clientConfig.authorizeURL))
-		req.params["grant_type"] = "refresh_token"
+		req.params["grant_type"] = OAuth2GrantTypes.refreshToken
 		req.params["refresh_token"] = refreshToken
 		if let clientId = clientId {
 			req.params["client_id"] = clientId
@@ -423,11 +424,11 @@ open class OAuth2: OAuth2Base {
 		}
 
 		let req = OAuth2AuthRequest(url: (clientConfig.tokenURL ?? clientConfig.authorizeURL))
-		req.params["grant_type"] = "urn:ietf:params:oauth:grant-type:token-exchange"
+		req.params["grant_type"] = OAuth2GrantTypes.tokenExchange
 		req.params["audience"] = audienceClientId
-		req.params["requested_token_type"] = "urn:ietf:params:oauth:token-type:refresh_token"
+		req.params["requested_token_type"] = OAuth2TokenTypeIdentifiers.refreshToken
 		req.params["subject_token"] = refreshToken
-		req.params["subject_token_type"] = "urn:ietf:params:oauth:token-type:refresh_token"
+		req.params["subject_token_type"] = OAuth2TokenTypeIdentifiers.refreshToken
 		req.add(params: params)
 
 		return req
@@ -512,12 +513,12 @@ open class OAuth2: OAuth2Base {
 		}
 
 		let req = OAuth2AuthRequest(url: (clientConfig.tokenURL ?? clientConfig.authorizeURL))
-		req.params["grant_type"] = "urn:ietf:params:oauth:grant-type:token-exchange"
+		req.params["grant_type"] = OAuth2GrantTypes.tokenExchange
 		req.params["resource"] = resourceUrl.appendingPathComponent(resourcePath).absoluteString
 		req.params["scope"] = clientConfig.scope
-		req.params["requested_token_type"] = "urn:ietf:params:oauth:token-type:access_token"
+		req.params["requested_token_type"] = OAuth2TokenTypeIdentifiers.accessToken
 		req.params["subject_token"] = accessToken
-		req.params["subject_token_type"] = "urn:ietf:params:oauth:token-type:access_token"
+		req.params["subject_token_type"] = OAuth2TokenTypeIdentifiers.accessToken
 		req.add(params: params)
 
 		return req
diff --git a/Sources/Flows/OAuth2ClientCredentials.swift b/Sources/Flows/OAuth2ClientCredentials.swift
index dc44e4e..eb5e8c3 100644
--- a/Sources/Flows/OAuth2ClientCredentials.swift
+++ b/Sources/Flows/OAuth2ClientCredentials.swift
@@ -21,6 +21,7 @@
 import Foundation
 #if !NO_MODULE_IMPORT
 import Base
+import Constants
 #endif
 
 
@@ -30,7 +31,7 @@ Class to handle two-legged OAuth2 requests of the "client_credentials" type.
 open class OAuth2ClientCredentials: OAuth2 {
 	
 	override open class var grantType: String {
-		return "client_credentials"
+		return OAuth2GrantTypes.clientCredentials
 	}
 	
 	override open func doAuthorize(params inParams: OAuth2StringDict? = nil) {
diff --git a/Sources/Flows/OAuth2CodeGrant.swift b/Sources/Flows/OAuth2CodeGrant.swift
index f97a40a..8d01288 100644
--- a/Sources/Flows/OAuth2CodeGrant.swift
+++ b/Sources/Flows/OAuth2CodeGrant.swift
@@ -21,6 +21,7 @@
 import Foundation
 #if !NO_MODULE_IMPORT
 import Base
+import Constants
 #endif
 
 
@@ -34,11 +35,11 @@ key will be embedded into the request body.
 open class OAuth2CodeGrant: OAuth2 {
 	
 	override open class var grantType: String {
-		return "authorization_code"
+		return OAuth2GrantTypes.authorizationCode
 	}
 	
 	override open class var responseType: String? {
-		return "code"
+		return OAuth2ResponseTypes.code
 	}
 	
 	
diff --git a/Sources/Flows/OAuth2DeviceGrant.swift b/Sources/Flows/OAuth2DeviceGrant.swift
index c838dac..b70089a 100644
--- a/Sources/Flows/OAuth2DeviceGrant.swift
+++ b/Sources/Flows/OAuth2DeviceGrant.swift
@@ -21,12 +21,13 @@
 import Foundation
 #if !NO_MODULE_IMPORT
 import Base
+import Constants
 #endif
 
 /// https://www.ietf.org/rfc/rfc8628.html
 open class OAuth2DeviceGrant: OAuth2 {
 	override open class var grantType: String {
-		return "urn:ietf:params:oauth:grant-type:device_code"
+		return OAuth2GrantTypes.deviceCode
 	}
 	
 	override open class var responseType: String? {
@@ -39,7 +40,7 @@ open class OAuth2DeviceGrant: OAuth2 {
 		}
 		
 		let req = OAuth2AuthRequest(url: (clientConfig.tokenURL ?? clientConfig.authorizeURL))
-		req.params["device_code"] = deviceCode
+		req.params["device_code"] = OAuth2GrantTypes.deviceCode
 		req.params["grant_type"] = type(of: self).grantType
 		req.params["client_id"] = clientId
 		return req
diff --git a/Sources/Flows/OAuth2ImplicitGrant.swift b/Sources/Flows/OAuth2ImplicitGrant.swift
index 3101f0b..7d6c310 100644
--- a/Sources/Flows/OAuth2ImplicitGrant.swift
+++ b/Sources/Flows/OAuth2ImplicitGrant.swift
@@ -21,6 +21,7 @@
 import Foundation
 #if !NO_MODULE_IMPORT
 import Base
+import Constants
 #endif
 
 
@@ -30,11 +31,11 @@ Class to handle OAuth2 requests for public clients, such as distributed Mac/iOS
 open class OAuth2ImplicitGrant: OAuth2 {
 	
 	override open class var grantType: String {
-		return "implicit"
+		return OAuth2GrantTypes.implicit
 	}
 	
 	override open class var responseType: String? {
-		return "token"
+		return OAuth2ResponseTypes.token
 	}
 	
 	override open func handleRedirectURL(_ redirect: URL) {
diff --git a/Sources/Flows/OAuth2PasswordGrant.swift b/Sources/Flows/OAuth2PasswordGrant.swift
index 02c7ef8..8f9a186 100644
--- a/Sources/Flows/OAuth2PasswordGrant.swift
+++ b/Sources/Flows/OAuth2PasswordGrant.swift
@@ -21,6 +21,7 @@
 import Foundation
 #if !NO_MODULE_IMPORT
  import Base
+ import Constants
  #if os(macOS)
   import macOS
  #elseif os(iOS) || os(visionOS)
@@ -53,7 +54,7 @@ If no credentials are set when authorizing, a native controller is shown so that
 open class OAuth2PasswordGrant: OAuth2 {
 	
 	override open class var grantType: String {
-		return "password"
+		return OAuth2GrantTypes.password
 	}
 	
 	override open class var clientIdMandatory: Bool {