Question: Who is the author of the book that has a musical adaption in which "Over the Rainbow" series in the United Kingdom was auditioning aspiring musical theatre performers for a role?

Context paragraphs:
The Wizard of Oz (1939 film): The Wizard of Oz is a 1939 American musical fantasy film produced by Metro-Goldwyn-Mayer.  Widely considered to be one of the greatest films in American history, it is the best-known and most commercially successful adaptation of L. Frank Baum's 1900 children's book, "The Wonderful Wizard of Oz."  It stars Judy Garland as Dorothy Gale, alongside Ray Bolger, Jack Haley, Bert Lahr, Frank Morgan, Billie Burke and Margaret Hamilton, with Charley Grapewin, Pat Walshe and Clara Blandick, Terry (billed as Toto), and the Singer Midgets as the Munchkins.

Over the Rainbow (2010 TV series): Over the Rainbow was a British television talent series that aired on BBC One from 26 March to 22 May 2010.  It documented the search for a new, undiscovered musical theatre performer to play the role of Dorothy Gale in Andrew Lloyd Webber's 2011 stage production of the 1939 film "The Wizard of Oz" and a dog to play Toto for a one-off performance.  Produced by Talkback Thames for the BBC, the series was presented by Graham Norton.  It followed previous collaborations between the BBC and Lloyd Webber to find new musical theatre performers: "How Do You Solve a Problem Like Maria? ", "Any Dream Will Do" and "I'd Do Anything".  The series was named after the song "Over the Rainbow" and was also aired by TV3 in Ireland.

Elle McLemore: Elle McLemore (born September 16, 1991) is an American actress.  She originated the roles of Eva in the Tony nominated Broadway musical production "Bring It On" and Heather McNamara in "Heathers", the musical adaption of the cult classic film of the same name.  She also starred in the final season of the television series "Army Wives".  In 2016, she played Patty Simcox in FOX's TV special Grease: Live.

John Kenrick (theatre writer): John Kenrick (born October 3, 1959) is an American author, teacher and theatre and film historian.  Kenrick is an adjunct teacher of musical theatre history at New York University, Brind School – University of the Arts (Philadelphia) and The New School, and lectures frequently on the subject elsewhere.  His 2008 book "Musical Theatre: A History" is a comprehensive history of musical theatre from ancient times to the present.  Kenrick is the curator of the extensive musical theatre and film website "Musicals101.com: The Cyber Encyclopedia of Musical Theatre, TV and Film"

Jennifer Gillis: Jennifer Kristine Gillis (born 26 April 1996) is a Canadian singer, dancer and actress with an extensive resume in musical theatre, television, singing, radio, recording, and animated voice-over work.  Gillis is most noted for performing in Sir Andrew Lloyd Webber's CBC TV reality show "Over the Rainbow"-a competition to be cast as the leading role of Dorothy Gale in Lloyd Webber's forthcoming production of "The Wizard of Oz" in Toronto, Ontario.  Being the youngest aspiring singer in the competition, she singularly represented her province of British Columbia and as a result was named the Top 6th musical theatre performer in all of Canada.  Since "Over the Rainbow", Gillis sang the Canadian national anthem "O Canada" for the Prime Minister of Canada, Stephen Harper on Parliament Hill in Ottawa, Ontario on Canada Day in 2013.  She aspires to become a Broadway actress someday and wants to dedicate her life to performing.

Love Birds (musical): Love Birds is an original musical with book, music and lyrics by Robert J. Sherman.  The musical officially premiered at the 2015 Edinburgh Fringe Festival at The Pleasance on August 7, 2015.  The production was directed and choreographed by Stewart Nicholls.  Prior to the Edinburgh run, there were two previews held in London at the Lost Theatre (in Stockwell) on July 28 and 29.  The Original Edinburgh Cast Recording was recorded on July 30 and mixed and mastered on July 31 and August 3 and was first released by SimG Records on August 12 at the Edinburgh Festival.  Two Edinburgh previews took place on August 5 and 6 with Press Night taking place on August 8.  The final festival performance took place on August 31.  The show starred Ruth Betteridge, Greg Castiglioni, John Guerrasio, George Knapper, Jonny Purchase, Joanna Sawyer, Anna Stolli, Rafe Watts and Ryan Willis.  In its end of the year round-up of regional British fringe musical theatre, "Musical Theatre Review" hailed "Love Birds": "a triumph of whimsy, a children’s story written with adult sensibilities and featuring a cracking score that celebrated the lost era of vaudeville.  Blessed with an equally strong design from Gabriella Slade and some marvellously sensitive performances, Love Birds was probably the most accomplished piece of musical theatre to arise from the many delights at this year’s festival."

Gerald Bordman: Gerald Martin Bordman (September 18, 1931 – May 9, 2011) was an American theatre historian, best known for authoring the reference volume "The American Musical Theatre", first published in 1978.  In reviewing an updated version of "American Musical Theatre" in 2011, "Playbill" wrote that the book had "altered the scope of American musical theatre history" and "remained the only book of its kind, and an invaluable one."

National Youth Music Theatre: The National Youth Music Theatre (NYMT) is an arts organisation in the United Kingdom providing pre-professional education and musical theatre stage experience for young people.  Based in London, it is constituted as a private limited company (originally named Children's Music Theatre Limited) and as a registered charity.  NYMT was founded in 1976 by director and playwright Jeremy James Taylor.  Since its inception, it has produced over fifty productions at the Edinburgh Festival Fringe, premièred thirty new musical theatre works, toured several times outside the United Kingdom, and had runs in the West End and on Broadway.  Amongst the many alumni of the National Youth Music Theatre who have gone on to careers in the performing arts are Jude Law (one of its patrons), Jonny Lee Miller, Sheridan Smith, Connie Fisher, Idris Elba and Matt Lucas.  Alumni have also included directors such as Jo Davies, and songwriters such as Tara Mcdonald.

Our Town (Producers' Showcase): Our Town is a 1955 episode of the American series "Producers' Showcase" directed by Delbert Mann and starring Frank Sinatra, Paul Newman and Eva Marie Saint.  The episode is a musical adaption of Thornton Wilder's 1938 play "Our Town", with songs by Jimmy van Heusen and Sammy Cahn.  It was Sinatra's only performance in a dramatic role specifically for television until "Contract on Cherry Street" in 1977.

Over the Rainbow (Canadian TV series): Over the Rainbow is a Canadian reality talent competition, which premiered on CBC Television on September 16, 2012.  Based on the 2010 series "Over the Rainbow" in the United Kingdom, the series auditioned aspiring musical theatre performers for the role of Dorothy for a Toronto production of Andrew Lloyd Webber's stage musical adaptation of "The Wizard of Oz".  The series was hosted by Daryn Jones.  Arlene Phillips, Thom Allison, and Louise Pitre served as judges alongside Webber.

Supporting paragraphs: Over the Rainbow (Canadian TV series) The Wizard of Oz (1939 film)
Answer: L. Frank Baum